Page 140 - PC2019 Program & Proceedings

PLANT CANADA 2019

S65. An inverse correlation between surface temperature and nitrogen rate predicted by a
thermodynamic theory
1
*1
Alzaben, H ; R. Fraser ; C. Swanton 2
1 University of Waterloo
2 University of Guelph

Crop stress can affect a plant’s ability to grow, develop and its ability to utilize and destroy solar exergy.
Exergy measures the energy quality, and is defined as the maximum useful to-the-dead-state
work. Consequently, exergy measures a system’s distance from equilibrium with the dead-state or
environment. Previous studies have utilized surface temperature as an ecological indicator for ecosystem
development. The more developed the ecosystem the cooler its surface temperature. In this study we
define our ecosystem as a corn field in which varying rates of nitrogen have been applied. It is
hypothesized that nitrogen stressed corn plants would be less developed and have higher surface
temperatures compared to non-stressed and more developed plants. The objective is to investigate
whether surface temperature can be used to identify nitrogen stress at an early growth stage as predicted
by the exergy destruction principle. Experimental trials were conducted at the University of Guelph Elora
Research Station in 2016, 2017 and 2018. Three spatial scales were investigated; leaf, canopy, and over a
plot area. Leaf and canopy temperatures were collected using an IR hand-held gun and a FLIR T620
thermal camera. A significant inverse correlation was observed between surface temperature and nitrogen
stress at a 0.05 significant level. A significant difference of less than 1 C was consistently observed
?
between stressed and non-stressed corn plants.

Heba Alzaben (halzaben@uwaterloo.ca)

S66. Photoperiodic injury in tomato is linked to circadian control of both nitrate assimilation and
ROS metabolism
Innes, G.; L. Tian; T.R.J.G Marie; M.E. Orozco; M.C. Micallef; B.J. Micallef
University of Guelph

Photoperiodic injury (PI) in tomato (Solanum lycopersicum L.) is characterized by chlorosis of vegetative
tissues when grown in extended photoperiods. The tomato cultivar ‘Micro-Tom’ is tolerant to PI whereas
the cultivar ‘Basketvee’ is PI-susceptible. A comparison of these two cultivars in photoperiods ranging
from 12 to 24 h light demonstrates a correlation between PI and accumulation of nitrite in leaf tissue.
Nitrite is a potentially toxic intermediary compound formed by nitrate reductase (NR) that is converted to
ammonium by nitrite reductase (NiR) during nitrate assimilation. The PI-tolerant cultivar ‘Micro-Tom’
maintained normal circadian rhythms for NR and NiR activity even in 24-h light, whereas the enzyme
activities became arrhythmic in the PI-susceptible cultivar ‘Basketvee’. A reduced NiR/NR activity ratio
correlated with increased nitrite and protein nitrosylation. We then hypothesized that a reduction in the
NiR:NR ratio in leaves will cause the PI-tolerant ‘Micro-Tom’ to become susceptible to PI. To test this
hypothesis, we generated several transgenic ‘Micro-Tom’ lines that contain an antisense construct for
NiR. Transgenic lines with reduced NiR activity became more susceptible to PI. Genetic analysis showed
that PI-tolerance in ‘Micro-Tom’ is controlled by two genes including CAB-13, which is a light-
harvesting protein in photosystem II. Interestingly, circadian rhythms of ROS accumulation differed
between ‘Micro-Tom’ and ‘Basketvee’. A model showing the involvement of both nitrate assimilation
and ROS metabolism in PI will be presented.

Barry Micallef (bmicalle@uoguelph.ca)

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