Sink-source imbalance triggers delayed photosynthetic induction: Transcriptomic and physiological evidence

Area of Science:

• Plant Physiology
• Molecular Biology
• Agricultural Science

Background:

• Sink-source imbalance leads to nonstructural carbohydrate (NSC) accumulation and photosynthetic downregulation.
• The direct cause of decreased photosynthesis—NSC accumulation or nitrogen deficiency—remains unclear.

Purpose of the Study:

• To investigate the relationship between photosynthetic capacity and NSC accumulation.
• To elucidate the impact of NSC accumulation on photosynthetic gene expression in Glycine max (soybean).

Main Methods:

• Inducing sink-source imbalance via cold girdling, sucrose feeding, and low nitrogen treatments in Glycine max and Phaseolus vulgaris.
• Analyzing transcriptome profiles in G. max to examine gene expression related to photosynthesis and NSC accumulation.

Main Results:

• NSC accumulation decreased maximum photosynthetic capacity and delayed photosynthetic induction in both species.
• In G. max, photosynthetic downregulation was linked to reduced expression of genes in the Calvin cycle, Rubisco activase, photochemical reactions, and stomatal opening.
• Sink-source imbalance may alter chloroplast sugar-phosphate translocator balance, promoting starch accumulation.

Conclusions:

• Photosynthetic downregulation is primarily triggered by NSC accumulation, not solely by nitrogen deficiency.
• Findings clarify the molecular mechanisms underlying photosynthetic impairment due to NSC accumulation in G. max.