Carbon Partitioning and Assimilation as Affected by Nitrogen Deficiency in Cassava

Abstract

Plants of cassava (Manihot esculenta Crantz) were raised in a sand root medium watered with nutrient solutions, under greenhouse conditions. As the N-supply increased, shoot dry mass was enhanced to a greater extent than root dry mass, thus leading to an increased shoot to root ratio. In leaves, contents of total soluble saccharides, non-reducing saccharides, and inorganic phosphate increased linearly with increasing N-supply. An opposite response was found for reducing saccharides and starch. In general, content of non-reducing saccharides was considerably greater than starch content. Activity of sucrose synthase was not detected, regardless of the N-treatments; by contrast, activity of neutral and acid invertases increased with increasing N-availability. Roots accumulated more total soluble saccharides, but less reducing saccharides and starch, as the N-supply increased. Photosynthetic rates decreased with increasing N-deficiency. Such a decrease was circumstantially associated to reducing saccharide, but not starch, accumulation. Results suggest a limited capacity for carbon export from source leaves under N-limitation.

<b>Salinity reduces carbon assimilation and the harvest index of cassava plants (<i>Manihot esculenta</i> Crantz)

“…Another important aspect, as deduced from a lower HI, is that the tuberous roots' ability to metabolize sucrose unloaded from phloem could have been impaired, leading sugar accumulation in the source leaves, which can determine photosynthesis inhibition, a process known as "photosynthetic repression feedback". This has already been observed in cassava by Cruz, Mosquim, Pelacani, Araujo, and DaMatta (2003). Albacete et al (2014) also indicated that the reduction in sink activity might be an indirect effect of salinity on A.…”

Rooting for cassava: insights into photosynthesis and associated physiology as a route to improve yield potential

“…Further, high N concentration also increases the concentration of cyanogenic glucosides in the root while decreasing starch (Obigesan & Fayemi, 1976;Howeler, 2002). The N use efficiency, but not yield, of cassava is often highest when plants are grown on soils with low N (Cruz et al, 2003). Several of the approaches discussed in the previous sections on improving photosynthetic efficiency would also increase N use efficiency, thus increasing production without the need for more N fertilizer .…”

Morphology, photosynthesis, and internal structure alterations in field apple leaves under hidden and acute zinc deficiency

“…This could be an adaptive response of the chloroplast to increase photosynthetic area and maintain photosynthetic rate under slight Zn deficiency. In the RL, owing to the damage of chloroplast membrane and extensive disorganization of thylakoids, the sucrose produced by chloroplast photosynthesis fails to be transported out of the cell (Cruz et al, 2003), thus, starch accumulated in the chloroplasts (Table 3, Fig. 3C, F and I), forming larger starch grains and depressing the feedback of Pn (Nafziger and Koller, 1976).…”