Journal
JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE
Volume 176, Issue 6, Pages 942-951Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/jpln.201200626
Keywords
anthocyanins; chlorophyll a fluorescence; gas exchanges; sweet basil
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Funding
- MIUR-PRIN (Ministero dell'Istruzione, dell'Universita e della Ricerca, Italy, Project Physiological response of vegetables crops to boron excess)
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This study was undertaken to investigate how different cultivars of sweet basil (Ocimum basilicum) responded to boron (B) excess. Two purple-leafed and eight green-leafed cultivars were hydroponically grown for 20 d with 0.2 or 20 mg L-1 B in the nutrient solution. Leaf B concentration, gas exchanges, chlorophyll a fluorescence, and oxidative stress were determined at the end of the treatment along with the severity of leaf necrosis. A range of tolerance to B toxicity was found: the green cultivars were more susceptible than the purple-leafed ones characterized by a higher constitutive anthocyanin concentration. In all the genotypes B excess resulted in oxidative stress as determined by accumulation of malondialdehyde by-products (MDA), reduced photosynthesis, and the occurrence of leaf burn. A close correlation was found between leaf B accumulation and oxidative stress, as well as between oxidative stress and the severity of leaf burn. Net photosynthesis (P-n) was reduced due to both stomatal and nonstomatal limitations in the green cultivars whereas the reduction of P-n in the purple leaves was only attributable to stomatal factors. Chlorophyll a fluorescence revealed a decrease in the maximum quantum yield of PSII (F-v/F-m) and in the electron transport rate (ETR) in plants grown with B excess although less reduction was observed in the purple genotypes. The quantum yield of PSII (phi(PSII)) decreased as a result of B toxicity only in the green cultivars. It is concluded that anthocyanins are involved in attenuation of the negative effects of B toxicity.
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