Assessment of leaf ultrastructure offers insights into mechanisms regulating sugarcane performance under low-phosphorus stress

Abstract

Detailed studies of plant responses to phosphorus (P) deficiency might reveal opportunities to improve sugarcane performance under nutrient stress, termed as P use efficiency. Then, we aimed through transmission electron microscopy to offer insights into the effects of varying P supply on leaf ultrastructural traits influencing photosynthesis and leaf area formation. Plants of the genotype RB86-7515 were cultivated under varying nutrient supply (0.0125, 0.05, 0.2 and 0.8 mM P) for 4 months. Diagnostic mature leaves were sampled to evaluate ultrastructural organization and P concentration. Leaf area and plant dry mass responded positively to increasing P rates and maximum values were attained at 0.55 mM P. Leaf P concentration increased as a function of nutrient supply, and the greatest area of diagnostic leaf and whole plant growth was associated with 1.80 g kg−1 P. Under severe deficiency (relative growth ≤ 30% and leaf P ≤ 0.90 g kg−1) generated with 0.0125- and 0.05-mM P, transmission electron microscopy revealed pronounced damages to leaf ultrastructure. In mesophyll cells, the changes were more intense under the lowest P rate, and included disintegration of the middle lamella, collapse of plasma membrane and distortion of thylakoids. Bundle sheath chloroplasts of the severely P-deficient plants exhibited, compared with those under 0.2- and 0.8-mM P, disorganization of lamellar membrane system. Collectively, these ultrastructural alterations offer insights into how P deficiency affects whole plant photosynthetic capacity and provide possible target traits at canopy level related to sugarcane P use efficiency.