Temporal and Spatial Regulation of Sucrose Accumulation in the Sugarcane Stem

Abstract

Sucrose accumulation has been studied extensively in sugarcane-an example of a highly productive crop plant with the capacity for storing large quantities of sugar. Initial recognition and characterisation of the enzymes involved in sucrose synthesis and cleavage led to widely accepted models of how sucrose transport and accumulation occur. Studies on cells in culture and on isolated cellular fragments initially supported and strengthened these models but more recently have revealed weaknesses in them. Biophysical measurements and anatomical, histochemical, and tracer dye studies further eroded the older models. Molecular studies are beginning to reveal details at the gene and transcriptional levels of the enzymes involved in sucrose transport and metabolism. Collectively, results of recent research indicate the need for a new sucrose accumulation model. A dynamic model of rapid cycling and turnover of sucrose between the vacuole and metabolic and apoplastic compartments explains much of the data, but details of how the cycling is regulated remains to be discovered. *A paper presented at a symposium honouring the late John Hawker, held at the 34th meeting of the Australian Society of Plant Physiologists, Broadbeach, Queensland, September 1994.

Differential Expression of Phenylalanine Ammonia-Lyase in Different Tissues of Sugarcane (Saccharum officinarum L.) during Development

“…The number of concentric and peripheral vascular bundles which are distributed within the stems increases consistent with stem growth. Previous studies have shown that fluctuation in enzyme activities and gene expressions alter many metabolites linked to stem development and subsequent sucrose accumulation (Moore 1995;Lingle 1999;Casu et al 2004Casu et al , 2007. Accumulation of PAL transcript in the bundle sheath may indirectly affect storage of sugar in the stem, because sucrose concentration starts to increase in the internodes as elongation ceases and PAL accelerate stem elongation by increasing the number of lignified vascular bundles.…”

Carbon Partitioning during Sucrose Accumulation in Sugarcane Internodal Tissue

“…First, we assumed that a11 the hexoses were in the cytosol, and consequently would represent the lowest potential specific activity for those pools. This would represent the maximum potential flux and exemplify an extreme, since it is known that the sugars are probably equally distributed between the cytosol and the vacuole (for review, see Moore, 1995). The specific activities were then used to calculate the flux from the hexose pools (Table IV).…”

“…Second, we assumed that the measured cytosolic volume in sugarcane internodal tissue was 10% (Komor, 1994), and that the distribution of sugars in the cell was equal (Moore, 1995), and then assumed that a11 of the label was largely restricted to the hexoses in the cytosol. This probably represents the lower limit of the flux from the hexose pool (highest potential specific activity), since at least some labeled hexoses will be present in the vacuole.…”

“…Although the carbon partitioning studies were conducted in vitro, we propose that this approach was adequate to assess the changes in symplastic metabolism associated with whole culm tissue. Precautions were taken to avoid most of the criticism previously leveled against the use of tissue slices in sugarcane (for review, see Moore, 1995). Precautions that were taken in our study included a prelabeling iso-osmotic wash buffer so as to not alter turgor (Lingle, 1989), variation in the duration of labeling experiments to ensure that the pattern of metabolism was not changing (for review, see Moore, 1995), an extensive postlabeling tissue wash to remove label associated with the apoplast (Lingle, 1989), and the extraction of tissues to investigate the partitioning only of the labeled substrates taken up by the cells.…”

Oligomerization, Membrane Association, and in Vivo Phosphorylation of Sugarcane UDP-glucose Pyrophosphorylase

“…Interestingly, in both of the cultivars, ScUGPase-1 expression in the internodes was modulated during the maturation process, with higher expression during the early stages of internode maturation, suggesting a possible role of ScUGPase-1 in cell wall biosynthesis. In addition, the elongation of sugarcane internodes is followed by increasing sucrose concentration (53). The accumulation of UGPase products decreases the protein activity (10).…”