The Different Photoprotective Mechanisms of Various Green Organs in Cotton (Gossypium Hirsutum L.)

Abstract

Photoinactivation of Photosystem II (PS II) during photosynthesis can lead to the loss of photochemical efficiency and decrease in crop yield. Plants have evolved various photoprotective strategies to ameliorate photoinactivation of PS II. Non-leaf organs of cotton also contribute to carbon gain, but it is not clear how they photoprotect themselves. This study investigated the photoprotective mechanisms in the leaf, bract, main stem and capsule wall of cotton. Our results suggested that the bract mainly relies on high activities of antioxidative enzymes and high ΔpH- and xanthophyll-regulated thermal dissipation (Φ_NPQ) for photoprotection. The main stem preferentially dissipated its absorbed light energy via light-regulated as well as light-independent non-photochemical quenching, aided by the moderately high activities of antioxidative enzymes. The capsule wall was less able to remove reactive oxygen species due to lower activities of antioxidative enzymes, and less able to dissipate energy via heat due to its lower Φ_NPQ. Its main photoprotective mechanisms seem to be (a) direct quenching of the energy by abundant carotenoids and (b) light-independent constitutive thermal dissipation via Φ_f,D. The green organs of cotton have different ways to use or dissipate energy.