Changes in Ratio of Soluble Sugars and Free Amino Nitrogen in the Apical Meristem During Floral Transition of Tobacco

Abstract

Under a modification of the nutrient diversion hypothesis, we propose that an inequality in carbohydrate and nitrogen translocation to the apical meristem may be a controlling factor in floral transition. Experiments were conducted in controlled-environment chambers to determine the associations between microscopic characteristics of the transition from vegetative to floral stages of the apical meristem of flue-cured tobacco and to assimilate concentrations in the plant and apical meristem. Low temperature, nitrogen withdrawal, and restriction of nitrogen uptake were used as treatment variables. In all of these stress treatments, flowering occurred at a lesser number of leaves than in control treatments. Low temperature stress accelerated the time of transition to the floral stage as compared with a high temperature control; however, nitrogen stress did not accelerate the time of transition. All stress treatments affected the levels of nitrogen and carbohydrate in whole plants. Most notable was an increase in the percentage of starch and a decrease in the percentage of total soluble carbohydrate induced by the stress treatments. These data indicate that tobacco plants under stress accumulate excess carbohydrate in the form of starch. An apparent inequality in the relative concentrations of carbohydrate and nitrogen in the apical meristem was observed in all treatments at the time of floral transition and is in support of the nutrient diversion hypothesis.

Transcript and metabolite signature of maize source leaves suggests a link between transitory starch to sucrose balance and the autonomous floral transition

“…Several lines of evidence support the hypothesized importance of the balance between transitory starch and sucrose in the leaf. First, an increase in the starch to soluble carbohydrate ratio is associated with floral promotion in day-neutral tobacco plants (Rideout et al , 1992). Further, tomato plants overexpressing SPS direct an increased proportion of newly assimilated carbon into sucrose synthesis at the expense of transitory starch accumulation.…”

Expression of sweet potato cysteine protease SPCP2 altered developmental characteristics and stress responses in transgenic Arabidopsis plants

“…The reasons and mechanisms are not clear. However, Raper et al (1988) and Rideout et al (1992) hypothesized that floral transition is stimulated by an imbalance in the relative availability of carbohydrate and nitrogen in the shoot apical meristem. Barth et al (2006) suggest that the flowering phenotype is likely linked to the endogenous ascorbic acid content.…”

Expression of Sweet Potato Senescence-Associated Cysteine Proteases Affect Seed and Silique Development and Stress Tolerance in Transgenic Arabidopsis

“…The reasons and mechanisms that sweet potato SPAE gene expression can promote earlier floral transition and enhance senescence in transgenic Arabidopsis plants are not clear. However, Raper et al (1988) and Rideout et al (1992) hypothesized that floral transition is stimulated by an imbalance in the relative availability of carbohydrate and nitrogen in the shoot apical meristem. Barth et al (2006) suggest that the flowering phenotype is likely linked to the endogenous ascorbic acid content.…”

“…The reasons and mechanisms are not clear. However, an imbalance in the relative availability of carbohydrate and nitrogen in the shoot apical meristem (Raper et al, 1988;Rideout et al, 1992), the change of endogenous ascorbic acid content (Barth et al, 2006), and possible nonspecific degradation and removal of flowering repressor(s) by ectopic SPCP2 expression are suggested.…”