Effects of treatments potentially influencing the supply of assimilate on its partitioning in sugarcane

Abstract

Two pot experiments and one field experiment were conducted on sugarcane to assess the effects of treatments expected to change total carbon assimilation on the partitioning of assimilate. In the first experiment pots of cultivars CP and N14 were arranged to simulate normal field spacing. At 5 months, plants were partially defoliated or left intact. In the subsequent four months, defoliation resulted in a small (not significant) decrease in total dry mass increment; it increased the proportional partitioning of assimilates to leaves in N14, whilst in CP it increased the proportional partitioning to stems. In both cultivars defoliation increased proportional allocation to non-structural dry matter, and thus sucrose, in the stem. In the second experiment pots of cv. CP were grown at normal spacing for 4 months, then left untreated, shaded, or placed further apart. During the subsequent four months shading decreased total dry matter increment, but increased proportional partitioning to the stems, and within stems to non-structural dry matter, and so sucrose. Widened spacing increased total assimilation, but decreased proportional allocation to stems; partitioning within the stems was not affected. In the field experiment plants of both cultivars were partially defoliated at 6 months, or left intact. Defoliation resulted in only a very small decrease in stem dry mass increment during the subsequent four months (leaves were not measured). Within the stem partial defoliation caused proportionally increased partitioning to non-structural dry matter, hence to sucrose. The results suggest that sucrose storage receives priority in the allocation of assimilate, rather than representing the accumulation of assimilate not required for vegetative growth.

Phloem Transport of Resources

“…This is a predicted response to a decreasing sucrose concentration difference between SEs and storage parenchyma symplasts, as sucrose concentrations of storage parenchyma cells rose during ripening (Table 12.1). Another characteristic difficult to reconcile with unloading by diffusion is the higher sink priority for sucrose storage over growth under reduced source/sink ratios (Pammenter & Allison 2002). Unloading by diffusion would cause a reversal of sink priorities under conditions of a reduced source/sink ratio.…”

“…Equilibrium will ultimately be reached between sucrose concentration differences driving diffusion back to SEs and rates of sucrose delivery by bulk flow. Regulation of bulk flow rates to sustain priority of sucrose accumulation under conditions of reduced source/sink ratios (Pammenter & Allison 2002) conceivably could be mediated by adjustments in PD hydraulic conductances or storage parenchyma turgors (Patrick & Offler 1996).…”

Regulation of photosynthesis by sugars in sugarcane leaves

“…The underlying mechanisms that govern feedback regulation between source and sink tissues are thus likely to be important in attempts to manipulate the stalk sucrose content. Pammenter and Allison (2002) have demonstrated, through measurement of structural and non-structural (i.e. sucrose) dry mass components, that both partial defoliation and shading result in a bias towards sugarcane culm sucrose accumulation, at the expense of structural growth of the stem.…”

Variação da fotossíntese e dos teores de carboidratos induzidos por etefom e déficit hídrico na fase de maturação da cana-de-açúcar

“…In sugarcane, growth suppression favors photoassimilate partitioning for storage (Chong et al, 2010), increasing the concentration of sucrose in the culm due to shading, partial defoliation, drought or cold (Huang et al, 2015;Li & Solomon, 2003;Pammenter & Allison, 2002;Robertson & Donaldson 1998). In this study, the imposition of drought did not affect the dry matter accumulation in the culms (Figures 3b,c) but decreased the concentration of sucrose in the culms of both varieties (Figures 5a,c).…”

“…Higher photosynthesis may be associated with higher demand for carbon by culms. In fact, culm is a high priority sink in the allocation of photoassimilates (Pammenter & Allison, 2002) and the activity of sinks in sugarcane regulates the activity of the source (Inman-Bamber et al, 2011). Thus, ethephon seems to have stimulated culm growth (Figure 3b), which started to accumulate more sucrose (Figure 5a).…”