Relações entre deficiência de potássio, metabolismo de açúcares e fotossíntese em plantas de algodoeiro

Abstract

Potassium (K+) is an essential macronutrient for plant growth and development, participating in vital functions such as stomatal conductance, photosynthesis and respiration. The increasing K+-deficiency in agricultural soils will lead to K+-deficiency in plants, and one of the problems caused is the accumulation of sugars in deficient leaves. View of this context, this research, was studied the disorder in photosynthetic metabolism of sugars in potassium deficiency and its recovery in leaves of different ages in cotton (Gossypium hirsutum L.). After germination, seedlings were transplanted into pots containing 2.8 L of Hoagland and Arnon’s solution (1950). The control (+K: 8.0 mM), K+-deficient (–K: 0.12 mM) and K+- recovery treatments were applied. The plant material was sampled after 23 days of treatment when it was observed reduction of photosynthesis in the first six leaves (F1 to F6, from the base). Immediately, the recovery treatment was applied to the remaining –K plants, and consisted in replacing the –K by +K solution. After 4 days of treatment, whole plant material was sampled. The youngest leaves were more susceptible to changes in growth, photosynthesis and sugars metabolism involved with potassium. On K+-deficiency, most of the K+ residual in oldest leaves was translocated to the younger. On K+-deficiency, although potassium had not varied between F1 and F5 leaves, there was a marked difference in dry matter production, leaf area, photosynthesis and sugars metabolism. Thus, the K+-critical levels that limited these processes were higher in young leaves. Due to the high Ci in deficient leaves, metabolic limitations appear to be the primary cause for reducing photosynthesis in F1 to F5 leaves. On the young leaves, the increased glucose was the only sugar which could be related to downregulation of photosynthesis in K+-deficiency. On the old leaves, reducing photosynthesis in K+-deficiency and recovery treatments was not related to the content of sugars. In young leaves, deprivation of potassium negatively affects growth, photosynthesis and sugars metabolism, but these processes could be recovered by removing up the deficiency. Old leaves are less susceptible to changes in these indicators, but are less susceptible to being recovered. It is concluded that similar potassium levels in leaves of different ages determine different responses to growth, photosynthesis and sugars metabolism, suggesting that these processes may have been modulated indirectly.