The activity of SnRK1 is increased in Phaseolus vulgaris seeds in response to a reduced nutrient supply.

Patricia Coello,Eleazar Martã­Nez-Barajas

doi:10.3389/fpls.2014.00196

Abstract

Phaseolus vulgaris seeds can grow and develop at the expense of the pod reserves after the fruits have been removed from the plant (Fountain etal., 1989). Because this process involves sensing the reduction of nutrients and the remobilisation of pod reserves, we investigated the effect on sucrose non-fermenting related kinase 1 (SnRK1) activity during this process. Bean fruits removed from the plant at 20 days after flowering (DAF) demonstrated active remobilisation of nutrients from the pod to the seeds. After 5 days, the pod dry weight was reduced by 50%. The process was characterized by a rapid degradation of starch, with the greatest decrease observed on day 1 after the fruits were removed. The pod nutrients were insufficient for the needs of all the seeds, and only some seeds continued their development. Those seeds exhibited a transient reduction in sucrose levels on day 1 after the fruits were removed. However, the normal level of sucrose was recovered, and the rate of starch synthesis was identical to that of a seed developed under normal conditions. Removing the fruits from the plant had no effect on the activity of SnRK1 in the pods, whereas in the seeds, the activity was increased by 35%. Simultaneously, a large reduction in seed sucrose levels was observed. The increase in SnRK1 activity was observed in both the cotyledon and embryo axes, but it was higher in the cotyledon. At 20–25 DAF, cotyledons actively accumulate storage materials. It is possible that the increase in SnRK1 activity observed in seeds developed in fruits that have been removed from the plant is part of the mechanism required for nutrient remobilisation under conditions of stress.

Highlights

Seed development is a complex and highly resource-demanding process that requires large amounts of C and N
Sucrose non-fermenting related kinase 1 (SnRK1) is a modulator of abscisic acid (ABA) functions, linking nutrient and/or energy state to ABA-regulated responses, and reduction in SnRK1 activity may cause either loss of ABA function and/or disconnection between metabolic signals and ABA, resulting in the prolonged expression of genes related to cell proliferation (Radchuk et al, 2006)
Bean pods have a significant amount of starch, and approximately one third of it is normally degraded in the period from 20 to 25 days after flowering (DAF)

Summary

Introduction

Seed development is a complex and highly resource-demanding process that requires large amounts of C and N. In cotyledons of Vicia faba, high glucose concentrations are found in non-differentiated regions, and glucose concentrations are low in mature starch-accumulating regions (Borisjuk et al, 1998). In V. faba cotyledons, protein accumulation occurs in the foremost regions, where ATP is more readily available, and starch synthesis is more active in the internal sections, where ATP levels are lower (Borisjuk et al, 2003). Sucrose non-fermenting related kinase 1 (SnRK1) is a modulator of abscisic acid (ABA) functions, linking nutrient and/or energy state to ABA-regulated responses, and reduction in SnRK1 activity may cause either loss of ABA function and/or disconnection between metabolic signals and ABA, resulting in the prolonged expression of genes related to cell proliferation (Radchuk et al, 2006)

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