Characteristics of Spinach Leaf Injury by Photochemical Oxidants and Mechanisms of Ozone Resistance in Spinach Cultivars (I)

Relationship of Growth Stages to Leaf In jury

Abstract

From spring to autumn each year in large areas of the Tokyo suburbs, spinach plants (Spinacia oleracea L.) are visibly damaged by atmospheric oxidants. Symptoms of this leaf injury are flecking on the upper surface of mature and lower leaves caused by ozone, or silver ing on the lower surface of mature leaves caused by peroxyacetylnitrate, or both.
Field susceptibilities to oxidants differed markedly among the 15 cultivars of spinach. Growth and bolting were more rapid in oxidant-sensitive than in resistant cultivars.
Spinach plant sensitivity to oxidants was generally low in the early stages of growth, increased toward harvest time, then gradually decreased toward senescence. Low-temperature treatment (4°C 14 days) at the sowing stage and gibberellin treatment at the growth stage of spinach plants accelerated aging and increased sensitivity to ozone.
Spinach leaf levels of total sulfhydryl groups, protein, and chlorophyll were higher in the early than in the late stages; this finding suggests that total sulfhydryl groups in spinach leaves are involved in the mechanism of protection against ozone toxicity.