Photooxidative Damage in Young Leaves of Declining Grapevine: Does It Result from a New and Possibly Viroid-Related Disease?

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Leaves of chlorotic plants of Vitis vinifera were investigated for physiological and ultrastructural disorders by comparing them with leaves of apparently healthy plants from a vineyard, where infection with Hop Stunt Viroid F (HSVdg) and Grapevine Yellow Speckle Viroid I (GYSVd1) was widespread. In affected plants, chlorosis was much stronger in young and developing than in old and fully expanded leaves. Chemical analyses failed to reveal mineral deficiencies. The quantum yield of photosynthesis was decreased in chlorotic leaves. A decrease in the number of PSI reaction centers was also observed. Persisting photoinhibition occurred only in leaves of affected plants. The redox state of cellular and extracellular ascorbate and increased levels of glutathione indicated oxidative stress in affected plants. Ultrastructural analysis revealed both swelling and loss of thylakoids even in young chlorotic leaves and other pathological changes. Symptoms were similar to those normally observed only in old senescing leaves. However, chlorotic leaves showed unexpectedly high protein levels, though aging is known to lead to protein degradation.
日本植物生理学会の論文