Single-leaf photosynthesis is a fundamental process in plant biomass production, and is a major research topic in crop physiology. This paper reviews the recent achievements of research on the physiological determinants of the photosynthetic capacity from the perspective of energy flow and CO2 diffusion. Measurement of chlorophyll fluorescence is a popular method to diagnose the function of photosystem II, and is useful to assess the susceptibility to photoinhibition and allocation of energy, which are keys to improving both stress resistance and photosynthetic productivity. Mesophyll conductance (gm) is the conductance to CO2 diffusion from intercellular airspaces to the chloroplast, and was long thought to be determined by leaf anatomical properties. However, recent studies showed that environmental conditions affect gm. It is possible that gm is affected by the gating of the CO2-permeable aquaporins (cooporins). Stomatal morphology is revealed to be an important factor affecting gas exchange both in crop plants and in Arabidopsis thaliana. The knowledge of the stomatal differentiation in Arabidopsis will be applicable to various crops. gm, stomatal conductance (gs) and leaf nitrogen content are the main factors to cause difference in leaf photosynthesis among rice lines, and recent activities are conducted to find genes to manipulate these factors. Although the association of leaf photosynthesis with crop productivity still has a large ‘missing link’, these achievements strongly suggest that the leaf photosynthetic capacity can be genetically improved in crop species.
The effect of high red/ far-red ratio (R/FR) on tillering in wheat and its cultivar differences were investigated with a pot experiment. Four Japanese wheat cultivars with a different degree of winter habit: Abukumawase, Sanukinoyume 2000, Norin 61 and Iwainodaichi, were grown under the tunnels with different R/FR conditions: one tunnel covered with a light control film which attenuates irradiance in the far red range (high R/FR) and the other with a transparent polyethylene film with a white shading cloth (control). The high R/FR treatment increased R/FR by 25%, and slightly decreased air temperature. The low temperature in high R/FR had some effect on the time of the developmental stage; however, physiological responses to high R/FR and its cultivar differences were observed. Tillering dynamics was quantified and analyzed based on phyllochron, site-filling and the time of cessation of tillering. The high R/FR significantly delayed the time in calendar days of full expansion of flag leaf and anthesis, but the effect of treatment was not significant in growing degree days. The high R/FR had no significant effect on the phyllochron and the maximum number of leaves on the main stem. The maximum number of tillers per plant was significantly increased and the cessation of tillering was significantly delayed by the high R/FR in all cultivars. In conclusion, the increase in the number of tillers in the high R/FR was attributed mainly to the delay of the cessation of tiller emergence, along with the significant increase in rate of tillering in some cultivars.
Phellogen (cork cambium) usually produces cork tissue, but when flooded it produces secondary aerenchyma, comprising living cells with non-suberized walls in the stems, roots, and root nodules of some Fabaceae. In the cell walls of cork tissues, the plant hormone abscisic acid (ABA), promotes suberin deposition. Thus, ABA may decrease in flooded tissues, where secondary aerenchyma cells are developing. Here, we investigated whether ABA is involved in the formation of aerenchyma in soybean (Glycine max) hypocotyls when flooded. Hypocotyls flooded with water produced a large amount of secondary aerenchyma, and were highly porous. On the other hand, application of 1.0μM ABA suppressed the enlargement of phellogen-derived cells, thereby suppressing subsequent gas space formation, and then almost completely inhibited aerenchyma development. Berberine-aniline blue staining indicated that not only elongated cells in the secondary aerenchyma but also packed cells, which were formed under flooding with ABA, contained no suberized cell walls. Compared to non-flooded plants, the endogenous ABA concentration in the flooded hypocotyls was decreased to 50% within 24 hr, and the low level was maintained for at least 72 hr. In addition, phellogen developed at 48 hr after flooding and secondary aerenchyma was observed at 72 hr. These results indicate that secondary aerenchyma formation requires a decrease in negative regulator ABA in soybean plants, that is, ABA inhibits elongation of cells derived from phellogen in secondary aerenchyma formation such as internodal cell elongation of floating rice stems.
Potato tuber initiation and its growth are key processes determining tuber yield, which are closely related to stolon growth, and are influenced by many factors including N nutrition. We investigated the influences of different forms of nitrogen (N) on stolon and tuber growth in sand culture with a nitrification inhibitor during 2010 – 2011, and using two potato cultivars. Plants supplied with NO3-N (N as nitrate, NO3–) produced more and thicker stolons than those supplied with NH4-N (N as ammonium, NH4+) at tuber initiation stage. In the plants fed NO3-N, the stolon tips swelled or formed tubers earlier and produced more tubers than in those fed with NH4-N. However, no significant difference was observed among N forms in terms of tuber yield at harvest, this may have been because of the shoot growth rate at tuber initiation stage was lower in the plants fed NO3-N. During the tuber bulking stage, the difference in shoot DWs among N forms began to decrease, and the shoot DW of plants fed NO3-N was even heavier than those fed NH4-N in some cases. The influence of N form on potato plant growth may therefore vary with the potato growth stage.
The important role of auxin polar transport in the early growth stage of etiolated maize (Zea mays L. cv. Honey Bantam) seedlings was intensively studied. Rapid growth in the basal region of coleoptile and the apical region of mesocotyl was observed in etiolated maize seedlings in the dark. Indole-3-acetic acid (IAA) applied to the top of coleoptile substantially promoted the growth of coleoptile and mesocotyl dose-dependently, suggesting that endogenous IAA is responsible for the growth of coleoptile and mesocotyl in etiolated maize seedlings. Polar transport of radiolabeled IAA ([14C]IAA) in the coleoptile segment was significantly higher than that in the mesocotyl segment from etiolated maize seedlings. Auxin polar transport in the coleoptile and mesocotyl segments from etiolated maize seedlings increased with the growth of the seedlings from which the segments were excised. Maximum expression of the gene (ZmPIN1a) closely related to auxin polar transport was observed just prior to maximum levels of auxin polar transport in the coleoptile and mesocotyl segments. In addition, the growth rate was well correlated with the auxin polar transport and the expression of ZmPIN1a gene in coleoptile and mesocotyl of etiolated maize seedlings. These results strongly suggest that auxin polar transport regulated by ZmPIN1a protein is essentially required for the growth of coleoptile and mesocotyl in the early growth stage of etiolated maize seedlings.
The quality of rice grain has been deteriorating as a result of the high temperature during the ripening stage caused by global warming. Easy and effective methods of high-temperature treatment are essential for the analysis of high-temperature tolerance and to screen for tolerant strains. We have improved the open-top chamber (OTC) by adding a solar-heated air introduction tunnel (SAT). The air is warmed by solar radiation as it passes through the tunnel and then flows into the OTC. The increase in temperature in the OTC-SAT was powered by solar radiation. Thereby, the temperature in OTC-SAT rose during the day according to the distance from the air intake (the nearer, the higher). A more uniform increase in temperature of approximately 1.2ºC in the daytime was achieved by attaching a sloping wall and funnel-shaped air exhaust tunnel to the OTC-SAT to improve the air flow. The area of the high-temperature treatment was easily increased by increasing the width of the OTC-SAT; this finding might be useful for screening a large number of strains. The increase in the percentage of chalky grains by the use of OTC-SAT was similar to that obtained with the other treatment methods; the OTC-SAT will thus be useful for investigating high-temperature tolerance during the ripening stage, particularly in areas where the wind direction is stable. The use of an OTC with a funnel-shaped tunnel on both the air entrance and the air exit sides might be useful in areas where the wind direction is often reversed.
The plastic responses of fifteen Amaranthus tricolor L. cultivars to the natural climatic conditions across successive two years were investigated. The interactions between cultivars and climates showed significant effects on all variables examined. SAT-072 cultivar showed the lowest plasticity in both years. Principle component analysis revealed three components (PCs) associated with 67% of the total variation (PC1 = 36%, PC2 = 19%, PC3 = 12%). PC1 includes leaf color attribute a*(red pigment), and photosynthetic pigments (chlorophyll a, chlororphyll b, total chlorophyll), while PC2 accounts for leaf color attribute b* (yellow pigment), betacyanins, betaxanthins and betalains. Canonical discriminant analysis (CDA) was an effective method for clear separation or grouping of cultivars that may promote effective management and utilization in crop-breeding programmes. Overall, these findings suggest the necessity of further study to enrich amaranth cultivars with desirable traits.
A field experiment was conducted to examine the possibility of introducing winter legumes, hairy vetch and faba bean, as green manures to turmeric cropping in a temperate region. Hairy vetch shoots were incorporated to determine the effect of N and P added as green manure. Higher values in plant height and number of leaves of turmeric were observed in the treatment with incorporation of hairy vetch than in that without incorporation (no-incorporation) throughout the growth periods. The differences in total amounts of N and P of turmeric between incorporation and no-incorporation treatments were the highest on 15 October, when the amount was increased by 8.0 g N and 1.1 g P m–2 compared with the no-incorporation treatment. From September to October, curcumin content rapidly increased with rhizome thickening, and gradually increased. We also quantified the N and P contribution from faba bean residues to the succeeding turmeric. The total amounts of N and P in turmeric cultivated after incorporating shoot and root residues into previously cultivated faba bean field were 2.5 g N and 1.0 g P m–2, respectively, larger than incorporating only roots. In previously fallow field, the incorporation of the shoot increased the total amount of N and P in tumeric by 4.5 g and 1.9 g m–2, respectively, compared with that without incorporation. In the second year after incorporation, growth and nutrient uptake of the turmeric crop did not significantly differ from those without incorporation. In the temperate region, these winter legumes would be used as basal organic matters for turmeric production.
Sorghum cultivar ‘Kazetachi’ has a unique internode length pattern, with a wavy shape that changes depending on the cultivation environment. It is regarded as a suitable material for analyzing the environmental factors affecting internode elongation. This study was conducted to clarify the relation between the final internode length at harvest and the increment of stem growth to establish a method to elucidate stem growth during the growing season. To confirm the internode elongation pattern, we sampled plants when each leaf had just expanded. The leaf number, plant length, and collar height of plants in the field were measured during the growing season. The internode elongation pattern of ‘Kazetachi’ resembled that reported in sweet sorghum, indicating that the elongation period of each internode can be estimated by recording the leaf number during the growing period. By measuring the plant length and the collar height as an index of stem growth, we can easily estimate the rapid elongation period of internode, which can be a peak or a trough in the internode length pattern during the growing period. The collar height during the growing period can be estimated by measuring the leaf number in the growth stage and recording the length of internodes and leaf sheaths at harvest. Even the plant length can be estimated by adding the leaf blade length to these traits. However, the collar height seemed to be a better index of stem growth than the plant length.
Greater species diversity in natural ecosystems increases plant biomass production and stability. Intercropping is an agricultural practice that aims to accrue the benefits of species diversity by growing two or more species simultaneously in the same space. Functional group diversity is considered important for enhancing the beneficial effects of species diversity, but most previous intercropping studies used combinations of only two functional groups. Thus, we used three green manure species from different functional groups: sorghum (Sorghum bicolor (L.) Moench.), a C4 grass; crotalaria (Crotalaria juncea L.), a legume; and sunflower (Helianthus annuus L.), a forb. We examined the effects of intercropping on biomass, nutrient uptake, and their stability using a proportional replacement series in a field experiment for three years with four trials. The aboveground biomass was higher with dual and triple-component intercrops compared with sole crops; however, there were no superior effects of triple-component intercropping over dual-component intercropping. There were also no clear advantages of intercropping in terms of the nutrient uptake amount and stability.
‘Tachiayaka’ is a novel cultivar of rice (Oryza sativa L.) with short panicles that is suitable for use in whole-crop silage. It was selected from bulked progeny obtained from two backcrosses of ‘Hoshiaoba’ to F1 plants of ‘Chugoku 146’ (‘Hoshiaoba’) × ‘Gokutansui (00kosen11)’. The unhulled rice yield of ‘Tachiayaka’ was comparable to that of ‘Tachisuzuka’, a short-panicle cultivar with high digestibility in cattle, in multi-location trials over a wide area spanning the Hokuriku to Chugoku regions in Japan. The whole-crop yield and the maturity of ‘Tachiayaka’ were comparable to those of ‘Hoshiaoba’. These findings indicated the suitability of ‘Tachiayaka’ for cultivation across a wide area of Japan. The characters associated with lodging resistance in ‘Tachiayaka’, including lodging index, were superior to those of ‘Hoshiaoba’. The high lodging resistance of ‘Tachiayaka’ will enable its cultivation in regions where lodging occurs frequently.