Changes in growth and photosynthetic capacity of cucumber seedlings in response to nitrate stress

AUTOR(ES)
FONTE

Brazilian Journal of Plant Physiology

DATA DE PUBLICAÇÃO

2009

RESUMO

The effects of three nitrate levels - 14(CK), 56(T-1), and 140 mmol L-1 (T-2) - on growth and photosynthetic capacity of cucumber (Cucumis sativus L. cv. Xintaimici) seedlings grown in hydroponic culture were investigated. The results showed that at 12 d after treatment plant height, stem diameter, leaf area, and leaf number of cucumber seedlings were stimulated by 56 mmol L-1 nitrate, whereas were inhibited significantly by 140 mmol L-1 nitrate compared with CK. Short-term stimulation in photosynthetic rate occurred under T-1 treatment, and then recovered to the level of CK. Photosynthetic rate of T-2 seedlings significantly decreased over treatment course with respect to CK. Photosynthetic pigment content of T-1 and T-2 increased during the first 2 d, and gradually recovered to the level of CK thereafter. Chlorophyll a/b and carotenoids/chlorophyll of T-1 had no significant difference from CK during treatment period. During the first 4 d, there was no significant difference in chlorophyll a/b and carotenoids/chlorophyll between T-2 and CK. After 4 d, chlorophyll a/b of T-2 increased gradually, whereas carotenoids/chlorophyll decreased. Actual PSII efficiency (ΦPSII) and photochemical quenching (qP) of T-1 had no significant difference from CK, and non-photochemical quenching (qN) was a little higher than CK after 2 d. During the first 2 d, there was little difference in ΦPSII and qP between T-2 and CK. After 2 d, both ΦPSII and qP of T-2 decreased to a great extend. A significant increase in qN of T-2 occurred over treatment course. With respect to CK, Hill reaction activity of T-1 slightly decreased, and T-2 treatment resulted in a significant decrease of Hill reaction activity. This evidence indicates that high-level nitrate stress may reduce photosynthesis through its effects not only on stomatal conductance but on the photosynthetic apparatus.

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