The jasmonate-free rice mutant hebiba is affected in the response of phyA′/phyA″ pools and protochlorophyllide biosynthesis to far-red light

Abstract

Phytochrome (phy) A in its two native isoforms (phyA′ and phyA″) and the active (Pchlide⁶⁵⁵) and inactive (Pchlide⁶³³) protochlorophyllides were investigated by low-temperature fluorescence spectroscopy in the tips of rice (Oryza sativa L. Japonica cv Nihonmasari) coleoptiles from wild type (WT) and the jasmonate-deficient mutant hebiba. The seedlings were either grown in the dark or under pulsed (FRp) or continuous (FRc) far-red light (λ_a ≥ 720 nm) of equal fluences. In the dark, the mutant had a long mesocotyl and a short coleoptile, whereas the situation was reversed under FR: short mesocotyl and long coleoptile, suggesting that the effect is mediated by phyA. Under these conditions the WT displayed a short coleoptile and emergence of the first leaf. In the dark, the spectroscopic and photochemical properties of phyA, its content and the proportion of its two pools, phyA′ and phyA″, were virtually identical between WT and hebiba. However, the total content of protochlorophyllides was higher in the mutant. Upon illumination with FRc, [phyA] declined in the WT and the ratio between phyA′ and phyA″ shifted towards phyA″. In hebiba, the light-induced decline of [phyA] was less pronounced and the ratio between phyA′ and phyA″ did not shift. Moreover, in the WT, FRp stimulated the biosynthesis of Pchlide⁶⁵⁵, whereas FRc was inhibiting. In contrast, in the mutant, both FRp and FRc stimulated the synthesis of Pchlide⁶⁵⁵. This means that FRc caused the opposite effect in hebiba. This difference correlates with a slower photodestruction of primarily the light-labile phyA′ pool in hebiba.