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In-Depth Information
higher Kl
l
and transpirational cooling (higher T
c
-T
a
) but showed lower wa-
ter loss than low-osmotic adjustment genotypes.
Osmotic adjustment could play a significant role in maintaining tur-
gor potential and turgor-related processes, such as opening of the stomata,
photosynthesis, shoot growth and extension of roots in deeper soil layers.
Continued root growth leads to greater exploration of soil volume and
an enhanced water supply to the plant. Genotypic variability for osmotic
adjustment exists in vegetable crops. Srinivasa Rao and Bhatt (1992) no-
ticed better OA in tomato cvs. Arka Saurabh, Pusa Early Dwarf and Sioux,
thereby relatively higher yield in these cultivars under moisture deficit
condition. Furthermore, Srinivasa Rao et al. (1999) reported that OA in
four cultivars of tomato did not show any significant variation during first
week of drought stress, but after three weeks of stress the maximum OA of
0.17 MPa during flowering stage and 0.47 MPa during fruiting stage was
observed in Arka Meghali. During the vegetative stage, better recovery of
osmotic potential was observed in RFS-1 followed by Arka Meghali and
Pusa Ruby, however, during the fruiting stage, recovery was better in cvs.
Pusa Ruby, Arka Meghali and RFS-1.
9.3.3 CHLOROPHYLL FLUORESCENCE
Drought stress is known to inhibit photosynthetic activity in tissues due
to an imbalance between light capture and its utilization (Foyer and Noc-
tor, 2000). The decrease in the maximum quantum yield of PSII photo-
chemistry (F
V
/F
M
) implies a decrease in the capture and conversion rate
of excitation energy by PSII reaction centers and so, a reduction in PSII
photochemical efficiency indicating the disorganization of PS II reaction
centers under water stress conditions. In general, the harvested energy in
excess of that consumed by the Calvin Cycle must be dissipated to avoid
oxidative stress and may lead to decreased PSII performance (Wilhelm
and Selmar, 2011). (F
V
/F
M
) was not affected by drought in Calluna, but
a small (1.5%) yet significant decrease was seen in
Deschampsia
across
season. Photosystem II (PSII) is highly sensitive to light and down regula-
tion of photosynthesis under drought stress causes an energy imbalance in
the PSII reaction center leading to photoinhibition (Pastenes et al., 2005).
Mechanisms have evolved in the plant to protect from photoinhibition,
such as non photochemical quenching, transport to molecules other than
