The Effect of Defoliation on Carbohydrate, Protein and Leghaemoglobin Content of White Clover Nodules

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Abstract
Single white clover plants grown in pots of Perlite in a controlled environment and completely dependent on N2 fixation were defoliated to various degrees (46–85 per cent of shoot weight removed). The soluble protein content of nodules declined by about 20 per cent and leghaemoglobin content by 50 per cent in the first 4–7 d after defoliation but increased again to control levels as new leaf tissue appeared. In the short term (2–3 h) carbohydrate content of nodules declined to different extents depending on the severity of defoliation. The initial decline in N2 fixation and the respiration associated with it, appeared not to be related to the instantaneous carbohydrate content of nodules but rather to the supply of current photosynthate from the shoot. After 24–48 h, however, the carbohydrate content of nodules had declined to low levels, regardless of the severity (46 or 71 per cent shoot removed) of defoliation. As new leaf tissue appeared carbohydrate levels in all parts of the plant gradually recovered towards control levels. Microscopic examination of nodule sections indicated that only after very severe defoliation (80–85 per cent shoot removed) was nodule deterioration evident. Even here, as the plant established new leaves, the damage to nodules was repaired and no nodule loss was apparent.