Tropical regions are prone to seasonal rains that leave the soil water-logged for long periods. Studying the impact of long-term water-logging on root development is important for fruit tree cultivation in the tropics. Myrtaceae roots are known to develop a protective tissue called polyderm. Among many Myrtaceae fruit trees, we observed that wax apple roots bear the most number of polyderm layers. How do polyderm-bearing roots respond to water-logged condition? In this anatomical study, young and older root tissues of three-year-old wax apple trees grown in normal and long-term water-logged conditions were compared. Root specimens sectioned by freehand or with an ultramicrotome were stained and observed under a fluorescent or optical microscope. Under normal condition, up to 5 layers of polyderm layers, composed of alternating endodermis-like cell layers and thick-walled cell layers with lignin and suberin accumulation, were observed whereas in water-logged condition, polyderm layers got restricted to 2-3 layers. In young water-logged roots, lignin-like accumulation in the inner cortical cell wall was fewer than in normal roots. Aerenchyma developed dramatically in cortical area of roots grown in water-logged condition signaling the hypoxic nature of the soil environment. Decrease of polyderm layers in water-logged condition indicates the insignificance of adding new cell layers with modified cell walls beyond the endodermis. Further experiments must be carried out in varying degrees and periods of water-logging to understand the mechanism controlling cell wall modification in root tissues and to clarify the role of structural changes and its possible long run effects.
Cell wall is an important component which decides growth, volume, shape of plant cells. Alternation of its structure also affects various aspects of plant development. In this study, we obtained a cDNA clone encoding an α-L-arabinofuranosidase/β-D-xylosidase from avocado fruit. The clone, designated as PaArf/Xyl3A, contained 3,002 nucleotides which encoded 777 amino acid residues with a calculated molecular mass of 83.4 kDa. The deduced amino acid sequence contained a putative signal peptide. Calculated molecular mass of the truncated protein was 80 kDa consisting of 745 amino acid residues. In addition, there were two potential N-linked glycosylation sites, suggesting that PaArf/Xyl3A would be exported to the apoplast where the enzyme could hydrolyze on cell wall polysaccharides. Phylogenetic analysis showed that PaArf/Xyl3A clustered near other plant α-L-arabinofuranosidases/β-D-xylosidases exhibiting a preferential arabinosyl hydrolyzing activity against natural polysaccharides. These results indicated that the protein would be secreted from cytosol to cell wall (apoplast) and might act as an α-L-arabinofuranosidase against natural polysaccharides. Accumulation of the mRNA was detected in the fruit right after harvest and other active growing organs such as immature leaves, expanded young leaves, germinating seedling and roots. According to the expression pattern and the phylogenetic relationship, PaArf/Xyl3A might be involved in arabinose metabolism and change to cell-to-cell contact of avocado during cell division/proliferation stage.
Saving irrigation water and increasing crop productivity are critical issues in Egypt. A field experiment of intercropping system was conducted with the purpose of minimizing evaporation from soil surface in the Nile Delta. Monoculture of maize, cowpea, soybean, intercropping of maize/cowpea, and maize/soybean were compared. In intercropping plots seeds of maize and leguminous crops were sown on the same ridge alternately by zigzag planting. Leaf area index (LAI) of canopies, SPAD value of maize leaves, biological yield and grain yield, water use efficiency (WUE), and land equivalent ratio (LER) were investigated. Establishment of cowpea plants was extremely poor which indicated that cowpea was not suitable to the highly compacted soil. Canopy of maize/soybean had higher LAI (3.2) than maize-mono (1.7), which is a positive indicator to minimize the evaporation. SPAD values of maize leaves increased by intercropping with leguminous crops. However, grain yield of maize and soybean decreased by 34 % and 48 %, respectively, when intercropped. Although the production of individual crop was reduced by intercropping, the system slightly improved the total land productivity (LER = 1.16). WUE of maize/soybean was similar to maize-mono, but higher than WUE of soybean-mono plot. Considering maize as a main crop, since intercropping with soybean covered soil with higher LAI and improved LER, the zigzag intercropping system has possibility to reduce evaporation and maintain the crop productivity especially for the small scale farmers in the Egyptian Nile Delta.
We investigated salinity effect on growth, yield and quality of Wakegi (Allium wakegi A.) of Okinawa. We examined the effects of foliar application of different salt concentrations (0.02%, 0.1%, 0.2%, 1%, and 5% bittern) on the growth parameters, rate of leaf tip burn, soil and plant analyzer development (SPAD) value, mineral content, proline content, and sugar content during 2012 and 2013. In this study, with the exception of the number of tillers, none of the growth parameters were significantly influenced by the investigated salt concentrations in 2012 and 2013. With the exception of 0.02% bittern in 2012, an increase in the salt concentration resulted in a slight increase in the number of tillers. The rate of leaf tip burn decreased under saline conditions, whereas the SPAD value increased with increasing salt concentrations. With the exception of 5% bittern in 2013, an increase in the salt concentration resulted in a slight increase in N content. In 2012 and 2013, we found negative correlations between the rate of leaf tip burn and N content (r = −0.835 and r = −0.960, respectively), and positive correlations between the SPAD value and N content (r = 0.888 and r = 0.528, respectively). An increase in the salt concentration up to 1% bittern resulted in an increase in the proline content; in 2012 and 2013, the proline contents in the presence of 1% bittern were 1.75 times higher than those of the controls. The glucose and fructose contents increased in response to increasing salt concentrations, especially in the presence of 0.2% bittern in 2013. Our results suggest that the proline and sugar contents of Wakegi increase under saline conditions and function as osmolytes, thereby enabling the plant to survive. Thus, Wakegi of Okinawa could be cultivated under saline conditions and near seashore area for improving quality parameters without decreasing yield.
The critical post-pollination temperature that negatively affects cherimoya fertilization and subsequent fruit set was determined by regulating nighttime (1800–0900 h) temperatures from 4 to 35ºC. Fruit set, weight, symmetry, number of seeds, and total soluble solid contents were recorded, and anatomical observations were performed for pollen-tube growth and fertilized embryos. All flowers at 10–32ºC set fruit, whereas at 4–8ºC and 35ºC, the flowers often failed to set fruit. Fruit weight, symmetry, and number of seeds improved at 17–22ºC. Fruit set and number of seeds decreased below 8ºC: in these temperatures, pollen-tube penetration into embryo sac was significantly restricted. Below 6ºC, anthesis was often delayed, and embryo sacs hardly accepted pollen tubes. The limited fruit set below 8ºC may be caused by inhibition of pollen-tube growth and of embryonic development after fertilization due to the direct effect of low night temperatures. Overall, heating to maintain minimum night temperatures of 10ºC after pollination was found to be effective to prevent fruit set failure.