BSc- MSc

The study entitled “Controlled abiotic stress induction for biofortification in
tomato (Solanum lycopersicum L.) and its influence on the Phenylalanine ammonia
lyase (PAL) gene expression” was conducted at the College of Agriculture, Vellayani,
Thiruvananthapuram, during 2022-2023. The objective of this study was to know the
impact of application of mild soil moisture stress and elevated CO2 associated high
temperature for biofortification of tomato and its influence on the expression levels of
the key enzyme PAL, involved in the biosynthetic pathway of nutritionally relevant
secondary metabolites in tomato.
The experiment was conducted in a completely randomized design in pot culture
with four replications with tomato, variety “Vellayani Vijay”. Plants were maintained
under open field conditions (390 ppm) and under the elevated CO2 of 500 ppm in the
Open Top Chamber (OTC) facility at the Department of Plant Physiology. The study
consisted of four treatments (i) exposure to mild moisture stress [withdrawal of
irrigation for 2 days 1 month after transplanting] (T1), (ii) exposure of vegetative phase
to eCO2 (500 ppm) associated high temperature for 1 week, [1 month after
transplanting] (T2), (iii) exposure of the entire vegetative phase to eCO2 (500 ppm)
associated high temperature (T3) and (iv) control (T4) conditions. Observations on
physiological and biochemical parameters were taken 60 days after transplanting.
Growth parameters, yield, and quality were observed at the time of harvest. The
expression analysis of the PAL gene was done in leaf tissues of experimental plants
using Real-Time PCR after exposure to both stresses.
Plants subjected to mild moisture stress and eCO2 exposure showed a significant
reduction in RWC and % leakage. Exposure to mild moisture stress resulted in a
significant increase in all the biochemical parameters like reducing sugar (52.55%),
phenol content (68.7%), carotenoid (24.4%), alkaloid content (19.1%) and ascorbic acid
(12.6%) in leaf tissues of tomato. Exposure to mild moisture stress resulted in a
significant increase in all the biochemical parameters like reducing sugar (25.74%),
phenol content (76.9%), carotenoid content (84.2%%), alkaloid content (20.8%),
lycopene content (32.1%) and ascorbic acid (47.8%) in fruits. Elevated carbon dioxide
exposure to a period of 1 week also had a positive impact on phenol, lycopene, and
ascorbic acid in fruits though carotenoid and alkaloid contents showed a reducing trend
with this stress factor. Both stress factors resulted in a reduction in root weight, shoot
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weight, and total dry matter. The root/shoot ratio was found to increase under mild
moisture stress (14.28%).
Phenylalanine ammonia-lyase (PAL) is a key enzyme involved both in the
phenylpropanoid and flavonoid pathways. In the present study, PAL gene expression
showed 1.64, 1.96, and 3.39 fold increase under mild moisture stress, eCO2(1 week),
and eCO2 (vegetative phase) exposure respectively compared to control. Exposure of
tomato plants to mild moisture stress and elevated carbon dioxide showed an
upregulated PAL gene expression.
The result of the study showed that the application of mild moisture stress and
exposure to eCO2 for a short period can result in biofortification in tomato variety
Vellayani Vijay. Stress-induced overexpression of PAL can be associated with
increased accumulation of secondary metabolites. The findings of the current study will
help to develop low-cost strategies for biofortification in tomato which can make high
quality farm products available to low-income consumers.