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The respiration and vitality of ungerminated bi‐ and trinucleate pollen were studied in order to determine the influence of relative humidity and temperature on metabolic activity. The gas exchange, germination capacity and staining with tetrazolium bromide were followed under standardized conditions.A constant respiration rate occurred under conditions of high relative humidity (97%). Per mg pollen, the trinucleate grains of Compositae and Gramineae respired 2 to 3 times as intense as 6 species of binucleate grains. Per unit of pollen protein the differences were even larger. In contrast to binucleate pollen, the longevity of trinucleate pollen was very short and the ability to germinate was lost twice as fast as the respiration capacity. This limits the use of tetrazolium bromide as an indicator of viability.At reduced relative humidities respiration was strongly restricted, but the longevity of bi‐ and trinucleate pollen considerably increased.Pollen of Gramineae, however, was very sensitive to changes in relative humidity; short exposure to low relative humidity decreased both the vitality and the capacity to respire.

The role of endogenous gibberellin (GA) in seed and fruit development was studied with the use of the GA‐deficient ga‐1 mutant of tomato (Lycopersicon esculentum Mill. cv. Moneymaker). Flowers of the ga‐1 mutant were abnormal and sterile, but parthenocarpic fruit development was observed occasionally on the dwarf plants. A single application of GA4+7 restored the fertility of the mutant flowers and resulted in seed set. Development of GA‐producing and GA‐deficient seeds in GA‐deficient fruits was compared by pollination of ga‐1/ga‐1 flowers with wild‐type or ga‐1 pollen, respectively. In ga‐1/ga‐1 seed dehydration started about 1 week earlier than in Ga‐1/ga‐1 seeds. Ultimate fresh and dry weights of mature Ga‐1/ga‐1 seeds were higher than those of ga‐1/ga‐1 seeds and showed negative correlations with the total number of seeds per fruit. Total content and composition of seed proteins were not influenced by the GA‐deficiency. Germination of the mature seeds depended on embryonal GA synthesis and was not influenced by maternal GA production. Final fresh weight of the ga‐1/ga‐1 fruits was positively correlated with the number of seeds per fruit. In these fruits, the minimum number of seeds for growth above the parthenocarpic level was about 10 or 35 in the presence of Ga‐1/ga‐1 or ga‐1/ga‐1 seeds, respectively. Fruits containing GA‐producing seeds reached a higher fresh weight than those containing GA‐deficient seeds, and their ripening was delayed by one week. It is concluded that gibberellin is indispensable for the development of fertile flowers and for seed germination, but only promoting in later stages of fruit and seed development.

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