Page 214 - PC2019 Program & Proceedings

PLANT CANADA 2019

Listing of Abstracts for the Poster Program

TOPIC 1: Abiotic Stress (Posters P1-P24)

P1. Photoperiodic injury in tomato involves opposing short-term and long-term acclimation of
photosystem II operating efficiency and chlorophyll levels
Marie T.R.J.G. ; B. Grodzinski; B.J. Micallef
*
University of Guelph

Photoperiodic injury (PI) is an abiotic stress observed in tomato when exposed to continuous or non-24hr
artificial lighting photoperiods. After a week or more of treatment, chlorotic leaves and reduced biomass
become evident. Little is known about the connection between short-term (<24hrs) and long-term
(>5days) responses to PI. Light harvesting complex II (LHCII) has been implicated in tolerance to PI, and
it is important for balancing excitation between photosystem I (PSI) and photosystem II (PSII).
Chlorophyll (Chl) content and Chl a:b ratios were determined using in-vitro and in-vivo absorption-based
assays. Chlorophyll fluorescence, to calculate PSII operating efficiency (YII), was measured every two
hours over a two-week period using the automated PSP32 multi-probe plant stress monitor by Opti-
Sciences. PSI/PSII fluorescence ratio was used for assessment of stress and fluorescence-based in-vivo
Chl content. Under continuous light, both PI-tolerant and -intolerant cultivars showed similarity in short-
term acclimation, where Y(II), Chl content, Chl a:b ratio, and PSI/PSII ratio all increased. Long-term
acclimation decreased Chl a:b ratio; however, for the intolerant cultivar Chl content dropped, PSI/PSII
ratio continued to increase, and Y(II) plateaued lower to eventually destabilize.

Telesphore Marie (mariet@uoguelph.ca)

P2. Superoxide is diurnally rhythmic and dampens under continuous light in tomato
*
Marie T.R.J.G. ; M.C. Micallef; B. Grodzinski; B.J. Micallef
University of Guelph

Once exposed to continuous light, tomato exhibits photoperiodic injury (PI) that is visualized as
interveinal chlorosis and overall stunted growth. Radicals are one light-dependent chloroplastic
metabolite that may be involved. It is hypothesised that radicals are a signal of redox poise, integrating
metabolism between chloroplast and nucleus during light and dark cycles. Superoxide was assayed
diurnally in both PI-tolerant and -intolerant tomato cultivars using nitroblue tetrazolium staining (NBT).
The NBT protocol was modified to ensure homogenous infiltration of the substrate, providing a uniform
intensity dependent visualisation of superoxide content. Staining was confirmed to be intracellular and
light-dependent indicative of chloroplast localisation. Interestingly, plants grown under normal
photoperiods have more superoxide than those under continuous light during the day. Furthermore, the
difference in quantifiable superoxide content precedes visual chlorotic symptoms. Histological and image
analysis reveals superoxide content is diurnally rhythmic under a normal photoperiod, and the rhythm is
dampened under continuous light. A PI-tolerant cultivar shows more robust rhythms under continuous
light for clock-regulated parameters, including nitrate assimilation, amino acid levels, stem extension and
cotyledon movements. We propose that superoxide acts as an input to the circadian clock, which is
essential for entrainment of arrhythmic clocks in PI-intolerant cultivars.

Telesphore Marie (mariet@uoguelph.ca)

Page 212 of 339