Low light reduces saffron corm yield by inhibiting starch synthesis

Area of Science:

• Plant Physiology
• Agricultural Science
• Biochemistry

Background:

• Source-sink dynamics and starch synthesis in geophytes under low light are not well understood.
• Low light (LL) conditions can impact plant growth and yield, but specific mechanisms in saffron are unclear.

Purpose of the Study:

• To investigate the effects of low light on source-sink dynamics, carbohydrate metabolism, and corm yield in saffron.
• To elucidate the role of phytohormones and gene expression in mediating low light responses in saffron.

Main Methods:

• A two-year field experiment comparing natural light (NL) and low light (LL, 50% NL intensity) conditions.
• Analysis of corm yield, dry weight, carbohydrate concentrations (starch, sucrose, glucose), enzyme activities (invertase, sucrose synthase, ADP-glucose pyrophosphorylase), phytohormone levels (IAA, GA1, ABA), and gene expression (quantitative PCR and transcriptome analysis).
• Application of exogenous gibberellin A3 (GA3) to assess its impact on carbohydrate metabolism.

Main Results:

• Low light reduced corm yield by over 20% and decreased starch concentration in mother corms, while increasing sucrose and glucose.
• Under LL, leaves showed increased dry weight, while daughter corms had higher sucrose but lower glucose and starch concentrations.
• LL altered phytohormone levels (increased IAA and GA1, decreased ABA) and downregulated key genes involved in sucrose hydrolysis, starch synthesis, and ABA biosynthesis, while upregulating glycolysis and TCA cycle genes in leaves.

Conclusions:

• Low light decreases saffron corm yield by shifting resource allocation from mother to daughter corms and leaves.
• Elevated gibberellin and auxin, coupled with reduced abscisic acid under LL, promote leaf growth but inhibit carbohydrate metabolism in daughter corms.
• These hormonal and metabolic changes under low light ultimately suppress sucrose transport to daughter corms, reducing overall corm yield.