Physiology of rice tungro virus disease: Proline accumulation due to infection

Tungro virus infection stimulates proline accumulation in leaves of rice ( Oryza sativa L.), especially in a sensitive cultivar, Taichung Native 1. Disease‐induced proline accumulation increases with the severity of the disease. Proline also accumulates in senescing, detached healthy rice leaves. The magnitude of proline accumulation in these leaves was further accentuated by ABA and retarded by kinetin. In the absence of drought stress, virus infection induces severe symptoms (stunting) in a drought tolerant cultivar (Lalnakanda 41) when compared to cultivars with intermediate (MW 10) and high sensitivity (Cauvery) to drought. Thus tungro virus mimics water stress in inducing proline accumulation in rice leaves. In both cases a common factor, ABA, may mediate proline accumulation. In drought stress, proline accumulation is associated with tolerance, while in virus stress, proline accumulation is connected with sensitivity. It is, therefore, clear that proline cannot always act to relieve physiological stress.