Reduction in chloroplast number accounts for the decrease in the photosynthetic capacity of Mn-deficient pecan leaves

• Published in: Plant science (Limerick) Vol. 166; no. 4; pp. 1051 - 1055
• Main Author: Henriques, Fernando S.
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 01-04-2004; Elsevier Science
• Subjects: Biological and medical sciences; Carya illinoinensis; Chlorophyll fluorescence; Chloroplast peptides; chloroplasts; electron transfer; Fundamental and applied biological sciences. Psychology; Hill reaction; leaves; manganese; Metabolism; Mn deficiency; Pecan; pecans; photosynthesis; Photosynthesis, respiration. Anabolism, catabolism; photosystem II; plant nutrition; Plant physiology and development; quantum efficiency; Chlorophyll fluorescence; Q A; PSI, PSII; Chl; DPC; Chloroplast peptides; DCIP; Mn deficiency; Pecan; F 0, F M, F V; Hill reaction; Chlorophyll; Plant leaf; Juglandaceae; Carya illinoensis; Dicotyledones; Angiospermae; Spermatophyta; Photosynthesis; Chloroplast
• ISSN: 0168-9452; 1873-2259
• DOI: 10.1016/j.plantsci.2003.12.022

The effects of Mn deficiency on several chloroplast and photosynthetic parameters were investigated in pecan (
Carya illinoinensis (Wangenh.) C. Koch) leaves. The total chl content of Mn-deficient leaves was reduced to ca. one half of the control, but the chl a:b ratio underwent only a small decrease. Chloroplasts isolated from Mn-deficient leaves were as active as the controls in the photoreduction of DCIP using water as electron donor and the use of DPC as an alternative electron donor did not significantly increase the rates of dye reduction. The ratio of variable to maximum chl fluorescence decreased very slightly in Mn-deficient leaves, indicating that the intrinsic quantum efficiency of their PSII units was similar to that of controls. The polypeptide pattern of chloroplast internal membranes was identical in control and Mn-deficient leaves. Chloroplast numbers were found to be reduced in mesophyll cells of Mn-deficient leaves, but the Mn content of the chloroplasts remaining in these leaves were equal to those of controls.
It is concluded that in pecan leaves, the primary effect of Mn deficiency is a reduction in chloroplast numbers, and that the existing chloroplasts preserve their full photochemical competence. It is further concluded that this reduction in chloroplast numbers completely accounts for the decrease in pecan leaf’s photosynthetic capacity reported before, with no need to invoke additional PSII impairment.