Boron deficiency decreases growth and photosynthesis, and increases starch and hexoses in leaves of citrus seedlings

• Published in: Journal of plant physiology 2008-09, Vol.165 (13), p.1331-1341
• Main Authors: Han, Shuang, Chen, Li-Song, Jiang, Huan-Xin, Smith, Brandon R., Yang, Lin-Tong, Xie, Cheng-Yu
• Format: Article
• Language: English
• Subjects: Antioxidant; antioxidant activity; assimilation (physiology); Biological and medical sciences; boron; Boron - deficiency; carbohydrate content; carotenoids; Carotenoids - metabolism; chlorophyll; Chlorophyll - metabolism; Citrus; Citrus - drug effects; Citrus - growth & development; Citrus - metabolism; Citrus sinensis; electrolyte leakage; enzyme activity; fertilizer application; fruit trees; Fundamental and applied biological sciences. Psychology; gas exchange; hexoses; Hexoses - metabolism; Metabolism; nutrient solutions; oranges; Photosynthesis; Photosynthesis - drug effects; Photosynthesis - physiology; Photosynthesis, respiration. Anabolism, catabolism; Photosynthetic Reaction Center Complex Proteins - metabolism; plant biochemistry; plant nutrition; plant physiology; Plant physiology and development; Plant Proteins - metabolism; Plant Roots - growth & development; Plant Stems - drug effects; Plant Stems - growth & development; Plant Transpiration - drug effects; Plant Transpiration - physiology; protein content; seedling growth; seedlings; soil nutrients; starch; Starch - metabolism; stomatal conductance
• ISSN: 0176-1617; 1618-1328
• DOI: 10.1016/j.jplph.2007.11.002

Seedlings of sweet orange ( Citrus sinensis) were fertilized for 14 weeks with boron (B)-free or B-sufficient (2.5 or 10 μM H 3BO 3) nutrient solution every other day. Boron deficiency resulted in an overall inhibition of plant growth, with a reduction in root, stem and leaf dry weight (DW). Boron-starved leaves showed decreased CO 2 assimilation and stomatal conductance, but increased intercellular CO 2 concentrations. Activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), NADP-glyceraldehyde-3-phosphate dehydrogenase (NADP-GAPDH) and stromal fructose-1,6-bisphosphatase (FBPase) were lower in B-deficient leaves than in controls. Contents of glucose, fructose and starch were increased in B-deficient leaves while sucrose was decreased. Boron-deficient leaves displayed higher or similar superoxide dismutase (SOD), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR) and glutathione reductase (GR) activities, while dehydroascorbate reductase (DHAR) and catalase (CAT) activities were lower. Expressed on a leaf area or protein basis, B-deficient leaves showed a higher ascorbate (AsA) concentration, but a similar AsA concentration on a DW basis. For reduced glutathione (GSH), we found a similar GSH concentration on a leaf area or protein basis and an even lower content on a DW basis. Superoxide anion (O 2 − ) generation, malondialdehyde (MDA) concentration and electrolyte leakage were higher in B-deficient than in control leaves. In conclusion, CO 2 assimilation may be feedback-regulated by the excessive accumulation of starch and hexoses in B-deficient leaves via direct interference with chloroplast function and/or indirect repression of photosynthetic enzymes. Although B-deficient leaves remain high in activity of antioxidant enzymes, their antioxidant system as a whole does not provide sufficient protection from oxidative damage.