|Authors: ||K. Takayama, H. Nishina, Y. Sakai|
|Keywords: ||chlorophyll fluorescence, diagnosis, photosynthesis, reflectance, remote sensing, transpiration |
Early detection of physiological dysfunctions in plants caused by biotic or abiotic stresses is very important for the greenhouse management.
The objective of this study is to investigate the availability of PRI measurement technique for early detection of water stress induced photosynthetic dysfunction in tomato plant leaf.
Physiological (or Photochemical) Reflectance Index (PRI) has been used as a useful parameter that indicates the status of plant leaf stress in various research fields in recent years.
PRI is calculated with the reflectance at 531 nm and 570 nm, PRI=(R531-R570)/(R531+R570), and several previous studies reported that the changes in the reflectance at 531nm were correlated with the changes in de-epoxidation state of the xanthophyll cycle, which regulates the activation of heat dissipation of excessive light energy absorbed by chloroplasts.
Hence, PRI provides information on leaf photosynthetic activity, e.g.
PRI shows linear or curvilinear relationships with chlorophyll fluorescence parameters such as non-photochemical quenching (NPQ) and photosynthetic efficiency (ΦPSII), however, which is depending on plant species.
In this study, we simultaneously measured PRI, chlorophyll fluorescence parameters (NPQ and ΦPSII), photosynthetic rate and stomatal conductance of an attached tomato plant leaf during water stress treatment induced by cutting the petiole of the leaf in the air.
Then, the relationships between those parameters were analyzed.
Photosynthetic rate and stomatal conductance promptly decreased after the petiole cutting and reached to their lowest levels within 60 min.
This showed that the severe water stress was induced by the petiole cutting treatment.
During the water stress treatment, ΦPSII decreased slowly, though NPQ and PRI decreased immediately.
The results imply that the changes in PRI observed here reflected the changes in NPQ, i.e. activation of the heat dissipation process in leaf, and PRI measurement technique is useful for early detection of photosynthetic dysfunctions in plants.
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