EFFECT OF AL, CD AND CU INTERACTIONS ON PHOTOSYNTHETIC CHARACTERISTICS AND SUGAR CONTENTS IN BARLEY LEAVES DIFFERING IN AL TOLERANCE - Soil Ecology Research Developments - page 24

Table 2. Effect of the different Al, Cd and Cu
treatments on chlorophyll contents of barley leaves

Genotypes Treatments Chl content

(mg . g -1 )

Chl a content
(mg . g -1 )

Chl b content
(mg . g -1 )

Chl a/b

pH 6.5 1.18 0.79 0.39 2.03

pH 4.5 1.15 0.76 0.39 1.94

Al 1.09 0.71 0.38 1.87

Gebeina Al + Cu 1.04 0.67 0.37 1.81

Al + Cd 1.03 0.66 0.37 1.78

Al + Cu + Cd 1.08 0.70 0.38 1.84

pH 6.5 1.19 0.79 0.40 1.98

pH 4.5 1.15 0.75 0.40 1.88

Shang 70-
119

Al 1.03 0.67 0.36 1.86

Al + Cu 0.99 0.64 0.35 1.83

Al + Cd 0.98 0.62 0.36 1.72

Al + Cu + Cd 0.95 0.59 0.36 1.64

LSD0.05 Between genotypes 0.04 0.02 0.01 0.06

LSD0.05 Between treatments 0.03 0.03 0.01 0.05

Chl, chloropgyll.

3.3. Photosynthesis

The presence of Al, Cd, and Cu individual, binary and ternary in the culture medium all
decreased the net photosynthesis (Pn) and stomatal conductance (gs), but increased the
internal CO 2 concentration (Ci) in the stressed leave. The changes in Pn, gs and Ci were
maximum when plants were exposed to the ternary metals combination for Shang 70-119, but
the binary metals combinations for Gebeina (table 3). For instance, Pn under Al, Al + Cu, Al
+ Cd, and Al + Cd + Cu treatments was 87.3%, 84.1%, 84.1%, 86.2% and 83.4%, 79.1%,
79.7% 74.9% of the control for Gebeina and Shang 70-119, respectively. Thus, the decline in
Pn was associated with a parallel decrease in gs and increase in Ci, which was in agreement
with previous observations on cucumber under copper toxicity (Florence et al., 2002).
Similarly, Khudsar et al. (2001) showed that Pn and gs reduced significantly at 5-50 µg.g -1 Cd
treatments, but Ci also decreased obviously at 10 µg.g -1 Cd onwards. Up to a 53% decrease in
Pn was also found in the presence of 550 µmol.L -1 Al in two Triticosecal cultivars (Nunes et
al., 1995). However, Lidon et al. (1997) found an increase of 52% in gs in maize plants under
Al concentrations of up to 1 mmol. L -1 . Simon et al. (1994) also observed a similar response
in tomato plants, where Al at a 25 µmol L -1 concentration caused a 38% increase in the gs
value compared with the control. But at the highest concentration evaluated (50µmol L -1 ), a
62% decrease in the gs value compared with the control. Further, for Ci, Moustakas et al.
(1996) found a 10 % decrease of Ci in Thynopyrum bessarabicum in the presence of 1 mol L -
1 Al. Nevertheless, Dong et al. (2005) found that 1 µmol L -1 Cd and 10 µmol L -1 Cd toxicity
both increased Ci in tomato plants. In the present study, the increase in the metal toxicity in
growth medium decreased Pn and gs, but increased Ci, indicating that inhibition in Pn by
metal toxicity did not result from a stomatal closure.