Abstract
The irrigated agriculture at the São Francisco River Valley, Northeast Brazil, shows an increasing production of grapes for winery. Among the wines produced there the one obtained from Vitis vinifera L., cultivar Syrah, stands out due to its adaptation to the climatic conditions of the region. However, little is known about carbohydrates metabolism of vines cultivated in this region. The objective of this work was to evaluate sugar and starch contents and the invertase activity in vines leaves during two consecutive growing seasons. The experiment was carried out at Embrapa Semi-Árido and at Santa Maria Winery, respectively located in Petrolina and Lagoa Grande, Pernambuco-Brazil. Leaves were collected weekly from January to December of 2003 and assessed for reducing sugars, total soluble sugars and starch contents, as well as for acid (AI) and neutral invertases (NI). The results showed that reducing sugars, total soluble sugars and starch contents increased during fruit maturation and are influenced by temperature, radiation and insolation variations. The second growing season showed higher reducing sugars and total soluble sugars content and lower starch content in the leaves than the first one. AI activity was higher than NI activity and these also varied according to weather conditions. During berries ripening, leaves showed higher sugar content and invertase activity, suggesting a higher sugar metabolism and transport during this phase.
Highlights
Active source of tissues, such as mature leaves produce more carbohydrates than they require and export assimilates as sucrose to photosynthetically less active or inactive tissues, such as young leaves, roots, fruits or canes
Invertases are classified in three main groups: extra cellular invertases which are characterized by a low pH optimum, are ionically bound to the cell wall and are responsible for phloem unloading in growing tissues (Roitsch et al, 2003); vacuolar invertases which are soluble, are characterized by an acidic pH optimum and are shown to regulate vacuolar sucrose levels (Ohyama et al, 1995)
The supernatant was used for total soluble sugars and reducing sugars analysis and the pellet was used for starch extraction (Allen et al, 1977)
Summary
Active source of tissues, such as mature leaves produce more carbohydrates than they require and export assimilates as sucrose to photosynthetically less active or inactive tissues, such as young leaves, roots, fruits or canes. Among the carbohydrate metabolizing enzymes, the invertases are a group of β-fructosidases eventually classified according to the isoelectric point, pH optimum for activity (acidic, neutral or alkaline), solubility (soluble or insoluble) and cellular localization (Quick, 1996; Nascimento et al, 1998). Invertases are classified in three main groups: extra cellular invertases which are characterized by a low pH optimum, are ionically bound to the cell wall and are responsible for phloem unloading in growing tissues (Roitsch et al, 2003); vacuolar invertases which are soluble, are characterized by an acidic pH optimum and are shown to regulate vacuolar sucrose levels (Ohyama et al, 1995)
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