Abstract
The present investigation was undertaken in an attempt to elucidate the physiological basis of pollen degeneration caused by low temperature in some vegetable crops, such as green pepper, tomato, eggplant, melon and strawberry. The vegetables were grown in an unheated glasshouse during winter season, and green pepper and eggplant were grown also in a growth cabinet maintained at 20°C (Table 1). Temperature in the unheated glasshouse during the period of study was shown in Table 2. Just prior to anther dehiscence, one anther was taken from each flower for the determination of pollen fertility, and the remaining ones were used for chromatographic analyses of free amino acids. The analyses were repeated several times during the period of growing.
1. Pollen fertility, estimated by percentage of apparently viable pollen grains stainable with acetocarmine, decreased with the fall of temperature in vegetables grown in the unheated glasshouse, as shown in Table 4. The anthers of flowers blooming in the period from December or January to March was reduced in weight and contained only empty pollen grains or degenerating sporogenous tissue as well as in the case of hereditary male sterile plants reported in the previous paper (Fig.2 and 3; Table 3 and 4). In April, however, the apparently viable pollen grains increased in number according to the rise of temperature, and the pollen fertility reached more than eighty per cent. On the other hand, the anthers of vegetables grown in the growth cabinet of 20°C contained sufficient pollen grains of viable appearance, even in the severe cold season (Table 4).
2. Thirteen to fifteen ninhidrin-positive spots were detected in the chromatograms from fertile anthers of the vegetables grown in the growth cabinet of 20°C or in optimum temperature season (Fig. 1). Chromatographic differences were detected visually in the composition of some free amino acids between the fertile anthers and sterile ones caused by low temperature in the unheated glasshouse.
3. In every vegetable tested, correlation was found between pollen fertility and content of proline (Table 4). The chromatograms of fertile anthers had a amazingly large spot of proline, which was either lacking or very faint in the chromatograms of sterile anthers (Fig. 1). The result was in general agreement with that of the previous paper refering to the quantitative difference of proline recognized between fertile and hereditary male sterile anthers.
4. In addition, sterile anthers had smaller spot of alanine than fertile ones in tomato, and a larger spot of asparagine in green pepper (Fig. 1; Table 4-1 and 4-2). Such relations between the pollen fertility and content of alanine or asparagine were not recognized in the other vegetable crops tested.
5. In conclusion, it may be assumed that the low content of proline in mature anthers is related with the pollen degeneration, and amino acids play an important role for development of pollen grains in the vegetable crops tested in the present study.
