Potassium phloem unloading in late ripening grape berries of Vitis vinifera (L.) cv. Probus

Abstract

The aim of this investigation was to examine the possibility of using “berry-cup” technique to study K phloem unloading and accumulation of K in ripening grape berries, in field conditions. Investigations were conducted in two years. The new cv. Probus (V. vinifera cv. Skadarka x V. vinifera cv. Cabernet Sauvignon) was used. The “berry-cup” technique consists of a single peeled grape berry immersed in a cup which contains standard MES buffer. After 30 min. the buffer solution of the berry-cup was drained into a test-tube and the cup was filled with buffer again. This was done every 30 minutes, four times in total. The collected solution was used analysed for K content. Between 30 and 60 minutes, K concentration in solution decreased; this may be attributed to apoplast purging. After 90 and 120 minutes, K concentration in solution did not changed significantly: this represents K phloem unloading of the grape berry. Analysis of K concentration and pH in must was conducted at harvest. K concentration detected in the buffer solution after 120 min showed a significant negative correlation with K concentration in must (-0.69). Positive, but not significant correlation was found between K concentration and pH in must (0.64). The year had greatest impact on K phloem unloading, K concentration and pH in must. The presented technique was useful for field study of K phloem unloading in ripening grape berries. Thus, for further investigation, “berry-cup” technique can be used to study effects of environmental factors or viticultural practices on K phloem unloading and accumulation of K in ripening grape berries.