Further Studies On Post-flowering Photoperiod Responses Of Soybeans

Upon the former works of other researchers and the author, the evidences, varietal differences and physiological mechanism, especially the roles of endogenous hormones, of post-flowering photoperiod responses in soybean, were further studied in this report. The results were summarized as follows:1. The photoperiod responses of late soybean variety Zigongdongdou held in the full process from emergence to maturation, and photoperiod could regulate leaf senescence even the plants were depodded. The results showed that all transfers from short. days'(SD, 12h) to long days (LD, 18h), started from R1 (beginning bloom), R3 (beginning pod) and R5 (beginning seed), respectively, hastened the development and changed the agronomic characters of plants and chemical composition of seeds. SD hastening effects on flowering or maturation were also found in the photoperiod treatments conducted at the stages from VE (emergence) to V2 (completely unrolling of 1st trifoliate leaf), V2 to Rl, Rl to R8 (full maturity), R3 to R8, R5 to R8 and R6.(full seed) to R8. In the depodded plants, SD hastened senescence of leaves and the effect was related to the Maturity Groups of the varieties. It was proposed that the reversion of flowering plants to vegetative growth, when transferred to LD condition, was directly caused by the long photoperiod. \.2.The reversions of flower and inflorescence (raceme) were discovered and a new concept (overall reversion) of flowering reversion was proposed. Seedlings of a late-maturing soybean variety, Zigongdongdou (ZGDD), were treated with 8 to 10 SD of 12h immediately after the emergence, and then transferred to long LD (>15h). Terminal inflorescence (raceme) could be induced by SD, but the upper part of the inflorescence became stem, and a few floral primordia in the middle part of the inflorescence reversed to differentiate vegetative buds, because of the following LD after the SD induction. The phenomena mentioned above were the Ll)-induced inflorescence reversion and flower reversion in soybean plant. If the normal flowering plants of ZGDD were transferred to LD, the existed flowers and pods fell, fewer new flowers developed and the plants returned to vigorous vegetative growth. This phenomenon was designated by the concept of overall reversion, a new type of flowering reversion in plants. The discovery of flowering reversion is valuable in the study of pod bearing habit and ontogeny of soybean plants, and will be helpful to establish a new system of experimental material in the study of photoperiod responses of plants.3. The sensitivity of pre- and post-flowering photoperiod responses indifferent ecotypes of Chinese soybean were compared. 12 representative varieties collected from main ecological regions in China were sown in spring in Nanjing and different, photoperiod treatments were carried out to compare pre- and post-flowering photoperiod response of the various ecotypes. The results indicated that theflowering of all varieties was highly hastened by SD (12h), and the maturation was evidently hastened (P<0. 01), too, in 10 of 12 varieties, except 2 early ones of Dongnong.36 and Taixingheidou. Under the condition of this experiment, post-flowering photoperiod response was more sensitive than pre-flowering response in summer-sown soybean varieties , other ecotypes responded more sensitively before flowering than after flowering. The correlation analysis showed that the sensitivity of photoperiod responses before and after flowering was positively correlated to the lengths of corresponding developmental stages in natural daylength. Longer vegetative period was beneficial to the increase of seed number and seed yield per plant, and longer reproductive period was beneficial to the increase of lOOseed weight. The relationship between the sensitivity of pre- and post-flowering photoperiod responses and daylength and other environmental factors was discussed.4. It was found that the growth period structure (GPS, the ratio of the length of reproductive period to that of vegetative period) of soybean varieties w; , closely related to pre- and post-flowering photoperiod response sensitivity (PRS , In the study, the relationship between GPS and pre- and post-flowering RPS of varieties with similar maturity dates and different flowering dates or the ones with similar flowering dates and difl rent maturity dates were studied. The results showed that the length of pre- or post-flowering period in natural photoperiod was positively correlated to PRS in the stages. Among the varieties with similar flowering dates, the length of reproductive period ^was positively correlated to the maturation hastening rate (MHR). Some varieties did not accord with the above rule, demonstrating that the relationship was complicated. When maturing at the similar dates, the spring- or summer-sown varieties with longer vegetative period had more seeds and higher yield per plant, and the ones with longer reproductive period had higher 100-seed weight and lower yield. Among the summer-sown varieties with similar flowering dates, the ones with longer reproductive period had higher 100-seed weight. In spring-sown varieties, no significant correlation between the reproductive period and agronomic characters was found.5. The endogenous hormones played important roles in pre- and post-flowering photoperiod responses of soybean. The results showed that ABA was higher in SD than in LD but GAlt3, GAi*s/ABA and DHZR were lower in SD, IAA did not change greatly. In SD, GAi.:? was negatively correlated with IAA and was positively correlated with ABA. IAA was negatively correlated with DHZR in LD. DHZR was positively correlated with ABA both in SD and LD. The changes mentioned above had the similar trend in different varieties or developmental stages. We proposed that, in the development of soybean, the total amount of promoting substances retained quite stable by their opposite changes of corresponding hormones, and a relative balance between growth promoting substances and growth inhibitors maintained. The hormonal balance, especially the ratio of GA to ABA, played important roles inphotoperiod responses of soybean.6. The changes of endogenous hormones in photoperiod aftei—effect, LD-induced i nf I orescence revers i on, photoper i od response of depodded p! ants and the hormona I role in photoperiod regulation on source-sink relation were studied. Pre-flowering SD treatment hastened post-flowering development of super-early soybean variety Dongnong 36 and decreased the contents of ABA and ZRr. in leaves after flowering. When the seedlings of Zigongdongdou were induced by SD conducted at seedling (VE ~ V2) and then transferred to LD, the content of 1AA in leaves at V2 and latter stages was higher and ABA was lower in the leaves of SD-induced plants than that, grown continuously under 15h. It was proposed that the amount of hormones could be regulated with negative feed-back after SD treatment. In the depodded plants, SD increased the contents of ABA and IAA in the leaves. The ratio of hormonal contents in leaves to that in filling seeds were lower in SD than that, in LD. The increase of 100-seed weight in'SD may be related to more partitioning of hormones in the filling seeds' than in leaves. Applications of GA? in SD , PP333, S?