Agriculture Reference
In-Depth Information
are the important indicators of plants photosynthetic capacity. In addition, the great
differences in Al, Cu or Cd tolerance have been found among plant species and genotypes
within a species (Wu and Zhang, 2003; Guo et al., 2004; Nikookar et al., 2005).
Therefore, this study was carried out to analyze the effects of Al, Cd, and Cu interactions
on several photosynthesis related characteristics, chlorophyll fluorescence and the
accumulations of photosynthetic carbohydrate in two barley genotypes differing in Al
tolerance. Further, the present investigation was designed to determine whether the growth
reductions in the Al-stressed barley plants observed in previous study (Guo et al., 2007)
resulted from a decline in total leaf area or a reduction in Pn, or both. Also, chlorophyll a, b
contents, PS activity, contents of sucrose and starch in leaves of stressed plants were
examined to determine if these factors contributed to the growth response and the different Al
sensitivity of two barley genotypes.
2.
M
ATERIALS AND
M
ETHODS
2.1. Plant Material, Growth Conditions and Treatments
The experiment was carried out in 2006 at Shaoxing University, Shaoxing, China. Two 2-
rowed winter barley (Hordeum vulgare L.) genotypes differing in Al tolerance were used, Al
tolerant cv. Gebeina and Al sensitive cv. Shang 70-119. The seeds were surface sterilized in
0.2% NaClO for 20 min, rinsed with distilled water 4 times and germinated in moist quartz
sand in a culture room. When seedlings grew the second leaf (10-day old), they were selected
for uniformity and transplanted to a modified Hoagland nutrient solution with the photoperiod
of 8/16h (day/night) and the temperature of 23±2°C throughout the experiment. One week
after transplanting to the basic solution culture, Al as AlCl
3
.6H
2
O, Cd as CdCl
2
, and Cu as
CuCl
2
.2H
2
O were added to the nutrient solution, and the solution pH was adjusted with HCl
to following 6 treatments: (1) pH 6.5 (control); (2) pH 4.5; (3) Al (100 µmol L
-1
Al, pH 4.5);
(4) Al + Cu (100 µmol L
-1
Al + 10 µmol L
-1
Cu, pH 4.5); (5) Al + Cd (100 µmol L
-1
Al + 10
µmol L
-1
Cd, pH 4.5); (6) Al + Cu + Cd (100 µmol L
-1
Al + 10 µmol L
-1
Cu + 10 µmol L
-1
Cd, pH 4.5). The solution pH in each container was adjusted every other day with HCl or
NaOH as required. The experiment was laid out in a completely randomized design with five
replicates. The nutrient solution in the growth container was continuously aerated with pumps
and renewed every 5 days.
2.2. Measurements and Statistical Analysis
The upper second fully expanded leaves were sampled for analysis of net photosynthesis
(Pn), stomatal conductance (gs), internal CO
2
concentration (Ci) and Fv/Fm, at 30 days after
treatments. The Pn, gs, Ci were determined by using a portable carbon dioxide infrared
analyzer, model CIRAS-1 (Analytical Development Co. Ltd., England). The measurements
were taken between 09:00 and 11:00 hours for the intact plants. The measurements of the
chlorophyll fluorescence emission kinetics were taken using a portable fluorometer, model
FMS2CIRAS-1 (Plant Efficiency Analyser, PEA, Hansatech Instruments Ltd., England). The
