Remobilisation of phosphorus fractions in rice flag leaves during grain filling: Implications for photosynthesis and grain yields.

Kwanho Jeong,Sigrid Heuer,Terry J Rose,Omar Pantoja,Daniel L E Waters,Lei Liu,Cecile C Julia,Matthias Wissuwa,Prasanta K Subudhi

doi:10.1371/journal.pone.0187521

Abstract

Phosphorus (P) is translocated from vegetative tissues to developing seeds during senescence in annual crop plants, but the impact of this P mobilisation on photosynthesis and plant performance is poorly understood. This study investigated rice (Oryza sativa L.) flag leaf photosynthesis and P remobilisation in a hydroponic study where P was either supplied until maturity or withdrawn permanently from the nutrient solution at anthesis, 8 days after anthesis (DAA) or 16 DAA. Prior to anthesis, plants received either the minimum level of P in nutrient solution required to achieve maximum grain yield (‘adequate P treatment’), or received luxury levels of P in the nutrient solution (‘luxury P treatment’). Flag leaf photosynthesis was impaired at 16 DAA when P was withdrawn at anthesis or 8 DAA under adequate P supply but only when P was withdrawn at anthesis under luxury P supply. Ultimately, reduced photosynthesis did not translate into grain yield reductions. There was some evidence plants remobilised less essential P pools (e.g. Pi) or replaceable P pools (e.g. phospholipid-P) prior to remobilisation of P in pools critical to leaf function such as nucleic acid-P and cytosolic Pi. Competition for P between vegetative tissues and developing grains can impair photosynthesis when P supply is withdrawn during early grain filling. A reduction in the P sink strength of grains by genetic manipulation may enable leaves to sustain high rates of photosynthesis until the later stages of grain filling.

Highlights

Phosphorus (P) is a key component of primary metabolites such as ATP, nucleic acids and phospholipids that are critical to central metabolism [1]
While grain P concentrations tended to be lower when P was withdrawn from the nutrient solution at anthesis (T1) or 8 days after anthesis (DAA) (T2), the proportion of total P in the grains tended to be higher, with a trend of increasing Phosphorus harvest index (PHI) with earlier withdrawal of P from the nutrient solution (Table 1)
Under luxury P supply the photosynthetic rate at 16 DAA had only declined significantly when P was withdrawn from the nutrient solution at anthesis (T1), and at maturity the photosynthetic rate in the control plants was significantly higher than the photosynthetic rates of plants in all other treatments (Fig 4B)

Summary

Introduction

Phosphorus (P) is a key component of primary metabolites such as ATP, nucleic acids and phospholipids that are critical to central metabolism [1]. Grabau et al [12] demonstrated in soybean (Glycine max) that increased P nutrition during seed filling led to delayed leaf senescence and higher grain yield, and the withdrawal of P from the nutrient solution during seed filling in canola (Brassica napus) led to a reduction in plant biomass and seed yield [13]. The premise of these studies was that developing seeds are strong sinks for P, and the remobilisation of P from vegetative tissues results in insufficient P for other processes necessary for continued growth such as photosynthesis

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