In situ pod growth rate reveals contrasting diurnal sensitivity to water deficit in Phaseolus vulgaris

The development of reproductive tissues determines plant fecundity and yield. Loading of resources into the developing reproductive tissue is thought to be under the co-limiting effects of source and sink strength. The dynamics of this co-limitation are unknown, largely due to an inability to measure the flux of resources into a developing sink. Here we use nuclear magnetic resonance (NMR) sensors to measure sink strength by quantifying rates of pod dry matter accumulation (pod loading) in Phaseolus vulgaris at 13-min intervals across the diel period. Rates of pod loading showed contrasting variation across light and dark periods during the onset of water deficit. In addition, rates of pod loading appeared decoupled from net photosynthetic rates when adjusted to the plant scale. Combined, these observations illustrate that the rate of pod development varies under water limitation and that continuous, non-invasive methodologies to measure sink strength provide insight into the governing processes that determine the development of reproductive tissues. Quantification of the rate of Phaseoluspod growth revealed contrasting impacts of water deficit during light and dark periods in pod-expansion and seed-filling phases of development.

Automated summary

This study uses nuclear magnetic resonance (NMR) sensors to measure the accumulation rate of pod dry matter in Phaseolus vulgaris and finds that the loading rate of pods shows different patterns under water limitation. Continuous, non-invasive methods to measure sink strength can provide insights into the processes that determine the development of reproductive tissues.