Effects of Enhanced Ultraviolet-B (UV-B) Radiation and Antioxidative-type Plant Growth Regulators on Rice (Oryza sativa L.) Leaf Photosynthetic Rate, Photochemistry and Physiology

Abstract

Elevated UV-B radiation deleteriously affects rice yields. The impacts of plant growth regulator (PGRs; ?-tocopherol, glycine betaine [GB] and salicylic acid [SA]) applications on higher plants have been the subject of many studies. However, little or no work has been carried out on rice responses to ?-tocopherol, GB or SA under UV-B stress conditions. This study determined the effects of ?-tocopherol (2.3 kg ha-1), GB (2.0 kg ha-1) or SA (12.9 g ha-1) application on rice leaf photosynthetic rate (PN), photochemistry and physiology under ambient and elevated UV-B conditions. Elevated UV-B decreased PN (17%), quantum yield (8%), electron transport rate (9%), total chlorophyll concentration (8%), plant height (12%), number of leaves (17%), pollen viability (6%), phenolic concentration (46%) and yield (21%). The applications of Alpha-tocopherol, GB or SA increased yield by 23%, 18% and 29%, respectively, under elevated UV-B. Application of PGRs increased leaf phenolic content thus rendering protection against elevated UV-B.