Source/Sink Relations of Abscising and Nonabscising Soybean Flowers

Abstract

The partitioning of recently fixed '4C to setting and abscising flowers within the axilary raceme of 'Clark' isoline Elt soybeans (Glycine max L. Men) was examied as a function of time after anthesis of individual flowers. In such racemes, the first four flowers showed a 17% abscission while the next four flowers showed 47% abscission.Source/sink relations offlowers I-IV (normally setting) were compared to those of flowers V-VIII (normally abscising) by pulse labeling source leaves with '4C02 and determining the radioactivity of individual flowers after a 4-hour chase period. conditions.The physiological mechanisms of soybean flower and pod abscission are not fully understood. Some studies have implied that reproductive abscission in legumes is hormonally mediated (6,8,12,14), while others have implied that it is related to> the availability of photosynthetic assimilates (4, 10, 11). However, since reproductive abscission occurs at a time when plant photosynthetic rate is relatively high and reproductive growth rate is relatively low, it appears not to be limited by the contemporary supply of photoassimilate.The objectives of the current work were to examine the partitioning ofrecently fixed carbon to normally setting and normally abscising flowers within a given soybean raceme. By examining this partitioning as a function oftime after anthesis ofindividual flowers, and in relation to the time of abscission, it was hoped to shed light on the mechanism of abscission.

Response of soybean yield components and allocation of dry matter to increased temperature and CO2 concentration

“…The largest concentration of pods and grains in the first branches (Conquista) or racemes (CG7484RR) can contribute to altering pod and grain competition between racemes. For example, there is evidence that the sequence of flowers influences the competition intra and inter-racemes for carbohydrates (Brun and Betts, 1984;Spollen et al, 1986;Stockman, 1988;Mosjidis et al, 1993;Kokubun, 2011). Thus, the increase in pods and grains in the first racemes of the T3 treatment of CG7484RR can potentially increase the competition for resources, explaining the observed variations (Fig.…”

Effects of Source/Sink Ratio and Cytokinin Application on Pod Set in Soybean

“…This is probably caused by a defi cient supply of photoassimilate to fl owers, which might be induced by a competition for photoassimilates among leaves, stems, nodules and reproductive organs (Brun and Betts, 1984;Antos and Wiebold, 1984). In the present study, therefore, we examined the effects of increased supply of photoassimilate to fl owers, which was manipulated by increasing the ratio of source (leaves) to sink (the number of nodes bearing fl oral buds).…”

“…By reducing this abortion, we might be able to increase pod and seed numbers, thereby increasing the yield (Kokubun, 2004). Many previous studies have focused on two possible factors that might be involved in regulating the abortion; availability of photoassimilate or nutrients (Brevedan et al, 1978;Antos and Wiebold, 1984;Brun and Betts, 1984;Heitholt, 1986aHeitholt, , 1986b and quantity of certain hormones (Huff and Dybing, 1980;Heindl et al, 1982;Spollen et al, 1986aSpollen et al, , 1986bCarlson et al, 1987;Yarrow et al, 1988;Kokubun and Honda, 2000).…”

“…Therefore, a strong competition for photoassimilate among plant organs can lead to a defi ciency of photoassimilate available to reproductive structures (Antos and Wiebold, 1984;Brun and Betts, 1984). Shading treatment during a period from fl owering to pod development signifi cantly reduced pod number (Kokubun, 1988;Kurosaki and Yumoto, 2003), but increase in light intensity by supplemental light or plant shape manipulation increased pod number (Schou et al, 1978;Kokubun, 1988).…”

Roles of Auxin and Cytokinin in Soybean Pod Setting

“…By reducing this abortion, it might be possible to increase the pod number, thereby increasing the yield (Kokubun, 2004). Numerous precedent studies showed two putative factors involved in controlling the abortion: availability of photosynthate or nutrients for pod development (Brevedan et al, 1978;Antos and Wiebold, 1984;Brun and Betts, 1984;Heitholt et al, 1986a, b) and availability of certain hormones (Huff and Dybing, 1980;Heindl et al, 1982;Spollen et al, 1986a, b;Carlson et al, 1987;Yarrow et al, 1988;Kokubun and Honda, 2000;Yashima et al, 2005). Within individual racemes, the pod set percentage of basal flowers is considerably higher than that of distal ones (Wiebold et al, 1981;Spollen et al, 1986a;Saitoh et al, 1999): this phenomenon appeared to be associated with the endogenous cytokinin content of flowers; the basal flowers contained a higher percentage of cytokinin than the distal flowers (Kokubun and Honda, 2000).…”