Plant Science 159 2000 107 – 115
Photosynthesis and antioxidant enzymes of phyllodes of Acacia mangium
Hua Yu, Bee-Lian Ong
Department of Biological Sciences, National Uni6ersity of Singapore, Lower Kent Ridge Road, Singapore
119260
, Singapore Received 11 January 2000; received in revised form 22 June 2000; accepted 3 July 2000
Abstract
Physiological processes are influenced by environmental factors and plant characteristics. The distribution of photosynthetic capacity of phyllodes of Acacia mangium Willd. seedlings was studied in relation to the in vivo photosystem II PSII function,
photosynthetic gas exchange, chlorophyll fluorescence and activities of antioxidant enzymes superoxide dismutase SOD and ascorbate peroxidase APX of phyllodes at different positions on seedlings. There was a vertical gradient in photosynthetic
capacity of phyllodes along the shoot. Phyllode 1 at the apex showed negative carbon uptake at PPFD lower than 400 mmol m
− 2
s
− 1
. High photosynthetic capacities, chlorophyll concentrations, DFF
m
, and q
P
were observed in phyllodes 4, 6 and 8. The high photosynthetic capacities of mature phyllodes could be attributed to the enhanced availability of CO
2
and the high efficiency of PSII in energy absorption and utilization. Total SOD and APX activities on a dry weight basis were highest at phyllode 1
and decreased as the phyllodes matured. The high photosynthetic capacity and low respiration loss in mature phyllodes could be important factors, responsible for the rapid establishment and fast growth of A. mangium in reforestation programs. © 2000
Elsevier Science Ireland Ltd. All rights reserved.
Keywords
:
Acacia mangium; Ascorbate peroxidase; Chlorophyll fluorescence; Photosynthesis; Phyllode position; Superoxide dismutase www.elsevier.comlocateplantsci
1. Introduction
Leaves undergo many anatomical, physiological and metabolic changes during development. Indi-
vidual leaves, located at different heights of a plant, contribute differently to the photosynthetic
production of the whole plant. The rate of photo- synthesis in teak Tectona grandis was low in
immature leaves, peaked in third or fourth leaves from shoot apices and declined in lower leaves
[1]. In Acacia auriculiformis, the maximum rate of CO
2
assimilation was observed in the eighth leaf from the shoot apex and the changes in the rate
of photosynthetic CO
2
assimilation paralleled that of stomatal conductance [2]. Light-saturating rates
of photosynthetic O
2
evolution of leaves of Chenopodium album decreased more steeply with
decreasing leaf position than the chloroplast num- ber per cell; the loss of photosynthesis in lower
leaves was ascribed both to the decrease in chloro- plast number and the reduced photosynthetic ca-
pacity of the remaining chloroplasts [3].
Reactive oxygen species ROS are formed in leaves during the whole ontogenetic process and in
response to stress [4], more so in immature leaves, as the lack of photosynthesis could result in a
smaller sink for energy. Both enzymatic and non- enzymatic defense systems in plants have evolved
to suppress the production and removal of such toxic active molecules [5 – 7]. Enzymatic defense
systems in plants involve the action of superoxide dismutase SOD, peroxidases including ascorbate
peroxidases APX and reductases. Both chloro-
Abbre6iations
:
APX, ascorbate peroxidase; DFF
m
, effective PSII efficiency under light-adapted conditions; F
v
F
m
, maximal potential photochemical efficiency of PSII under dark-adapted conditions;
1F
o
– 1F
m
, the excitation energy trapping capacity at the reaction center of PSII; PPFD, photosynthetic photon flux density; q
P
, photo- chemical quenching; NPQ, non-photochemical quenching.
Corresponding author. Fax: + 65-7792486. E-mail address
:
dbsongblnus.edu.sg B.-L. Ong. 0168-945200 - see front matter © 2000 Elsevier Science Ireland Ltd. All rights reserved.
PII: S 0 1 6 8 - 9 4 5 2 0 0 0 0 3 3 6 - 8
plastic and cytoplasmic compartments of leaves contain these enzymes. The two important antioxi-
dant enzymes in chloroplasts are SOD and APX, which allow the efficient detoxification of ROS
generated from photooxidation [7]. Though many studies have focused on the antioxidant responses
of plants to environmental stresses [4], not much work has been devoted to study such changes in
relation to leaf development.
In the present study, the photosynthetic perfor- mance and antioxidant responses of phyllodes ex-
panded petioles that form simple, photosynthezing laminae [8] of 220 day-old A. mangium Willd.
seedlings were investigated. The aims of this study were to understand the distribution of phyllode
photosynthetic capacity in seedlings and its rela- tionship with the in vivo PSII photosystem II
function and antioxidant response. A. mangium is a fast growing tree, with an increasingly important
role in reforestation programs. This study should enable an understanding of the physiological fac-
tors that contribute to the rapid growth and estab- lishment of the seedlings.
2. Material and methods
