Agriculture Reference
In-Depth Information
tolerant one. So, it can be concluded that the different responses to acid soil toxicity of
two barley genotypes may partly result from the different metals interactions in plant
seedlings.
Keywords:
Aluminum, Copper, Cadmium, Toxicity, Barley (Hordeum vulgare L.), Leaf
traits, Chlorophyll contents, Photosynthesis, Chlorophyll fluorescence, Starch, Sucrose
.
A
BBREVIATIONS
Al, -aluminum;
Cd,- cadmium;
Cu,- copper
;
Pb,- lead;
Zn, -zinc.
1.
I
NTRODUCTION
Acid soils have extended over 40% to 70% of the world's arable soils (Rengel, 1992). A
multi-element pollution except for aluminum (Al) on acid soil is detected in many areas
though Al is considered as the major factor constraining crop performance when soil pH is
lower than 5.5 (Chen et al., 2000). Many reports showed that Al can disturb cell metabolism
by inhibiting nutrients absorption, stomatal function, photosynthesis, respiration and altering
the activity and quantity of the key enzyme of various metabolic pathways of the treated-
plants. Nevertheless, there have been few reports about the combined effects of Al and other
heavy metals on plants on acid soil up to now except our previous study suggesting the
existed synergistic effect between Al and low amount of Cd in barley seedlings (Guo et al.,
2004)
Numerous authors suggest that the inhibition of plant growth detected in many plant
species subjected to Al or heavy metals stress is often associated with a reduction in net
photosynthesis, which in turn is closely associated with the decreases in stomatal conductance
(gs), green leaf area, and leaf chlorophyll contents. The stomatal conductance is one of the
main factors regulating CO
2
flow and leaf transpiration (Kozlowski and Pallardy, 1997;
Jones, 1998), while the ability to maintain the rate of photosynthetic CO
2
uptake under stress
treatment is fundamental for plant growth and production. On the other hand, a simple, non-
intrusive way to monitor the performance of the photosynthetic apparatus is to measure
chlorophyll fluorescence and the changes in the characteristics related to fluorescence, such
as initial fluorescence (Fo), maximum fluorescence (Fm), variable fluorescence (Fv), and the
ratio between them (Lichtenthaler and Rinderle, 1988). The inverse relationship between the
photosynthetic activity and the
in vivo
chlorophyll fluorescence was detected in many
situations (Krause and Weis, 1991). Furthermore, starch and sucrose are two main fixed
photosynthetic carbohydrates. During active periods of photosynthesis, starch is formed as
temporary storage form of fixed carbon and is deposited as starch granules in the chloroplast,
while the sucrose is transported to different organs and is the most commonly used
photoassimilate by plants (Verma and Dubey, 2001). Thus, the contents of starch and sucrose
