No abstract

The roles of acid invertases, pH optima about 5, and neutral invenase, pH optimum 7, have been examined during growth and maturation of stalks of sugar cane (Saccharum officinarum) and hybrid cultivars. Bound acid invertases are found in the outer space which includes the cell wall. A soluble acid invertase occurs in immature, elongating internodes, and is located both in the outer space and the vacuole of storage parenchyma cells. This enzyme disappears when internode growth ceases. The outer space component appears to be the major controller for dry matter input accompanying cell extension growth. The vacuolar component appears to be concerned with regulation of both turgor pressure and internal sugar pools. The neutral invertase increases during maturation. The level of enzyme activity correlates with the level of hexoses. This enzyme appears to be part of a system controlling sugar flux in mature storage tissue.

Laterally connected vascular bundles in the nodes of sugarcane (Saccharum species cv. Pindar) stalks allow a rapid redistribution of water across the stalk should the vascular continuity be partly disrupted. Tritiated water supplied to the roots exchanged rapidly between the xylem and storage tissue so that net movement up the stalk was slow. The half-time for exchange in a labeled stalk was about 4 hours so that the entire water content of a sugarcane stalk can turn over at least once in a single day. No rapid flux of sugar between xylem and phloem or xylem and storage tissue was detected. Functional xylem contained only low sugar concentrations: less than 0.3 % w/v in the stalk and less than 0.02% w/v in the leaf. Previous reports of high sugar levels (9 % w/v) in sugarcane stalk xylem reflect some degree of xylem blockage followed by a slow equilibration with free space sugars in the storage tissue.The path of water through a plant is generally considered to involve passage through the root cortex to the xylem and thence as a continuous column through the stem to the leaves. In the leaves water passes from the xylem through the mesophyll cells to the substomatal cavity. Such a path involves lateral transport in both the root and leaf but, apart from lateral redistribution of water in the stem when parts of the root system are subjected to reduced water potential (2, 12), there is little evidence for substantial lateral water movement in the stem. Hulsbruch (9) stated that water follows the path of least resistance through the plant, but considered that lateral movement from xylem elements of the stem was a minor component of the total flow.Sucrose levels in the fluid expressed from xylem elements of sugarcane may reach 8 to 9% w/v (7). Since transpiration rates in sugarcane commonly exceed 1 liter per stalk per day this flow through the xylem would transport some 100 g of sucrose to the leaves daily, which is 25 to 50 times more sugar than could be produced by photosynthesis in the same period.The purpose of this paper was to investigate the movement of water and sugars through sugarcane stalks in order to resolve the above anomaly. MATERIALS AND METHODSFour distinct approaches were involved and the methods can be summarized separately for each study. Three treatments were imposed to follow dye redistribution in the stalk. These were (a) an intact stalk; (b) a stalk with two opposing lateral cuts within an internode; and (c) a stalk with the two lateral cuts separated by a node. Within 5 min of exposure the leaves of the control plants were fully colored and all stalks were split longitudinally to observe dye distribution.Similar treatments were applied to intact plants so that transpiration rates could be monitored. TRITIUM MOVEMENT 1. Uptake. Two liters of tritiated water (1-2 mc) were added to a plant growing in a container as outlined above. Free drainage was allowed, and the drainage water was poured back into the container several times to provide uniform labeling around the roots. The container...

No abstract

Trehalase activity was detected in extracts of roots, leaves, and stalk tissue from sugar cane. The enzyme was not bound to cell particulates, and had a pH optimum of 6.2 and a Michaelis constant for trehalose of 1×10(-4) M. The level of enzyme detected in mature stalk tissue was too low to account for glucose transport into tissue slices. The enzyme level was high in immature stalk tissue in which the vacuolar sugar pool turns over rapidly. Trehalose synthesis and breakdown may be part of a system for transport of hexose out from the vacuole.