Table 1 The dates of tagging squares at different main-stem nodes and fruiting positions, sampling times, and heat units accumulated during
the period of square development in 1993 and 1994 Sampling monthday
Tagging monthday Heat units
b
°C Node-position
a
5 Days 10 Days
15 Days 20 Days
25 Days Flower
1993 723
728 82
87 812
813 317
8-1 718
730 84
89 814
725 819
8-2 819
311 731
8-3 85
810 815
820 825
825 311
728 82
87 812
10-1 817
723 817
309 83
88 813
818 729
823 10-2
823 314
728 12-1
82 87
812 817
– 821
301 88
12-2 813
83 818
823 828
828 308
1994 10-1
76 711
716 721
726 731
83 273
718 723
728 10-2
82 713
87 810
265 723
728 82
87 718
812 10-3
815 266
a
The two numbers represent main-stem node and sympodial branch position, respectively.
b
Daily heat units °C = [T
max
+ T
min
2]−15°C, where T
max
and T
min
are the maximum and minimum daily temperatures in degrees Celsius, respectively.
Data of Branch Positions 1 and 2 at Node 10 for each year and non-structural carbohydrates of the
three tissues of leaves, bracts, and floral buds in 1994 were also performed with the ANOVA to
determine differences between years and among tissues. Correlation coefficients between final boll
retention and floral-bud non-structural carbohy- drate content at different positions were also cal-
culated. The analyses of variance combined over the 2 years of this study indicated significant
differences between years for non-structural car- bohydrates of the bracts and floral buds. There-
fore, data were interpreted individually for each year. When the F-value was significant at P 5
0.05, the LSD test P = 0.05 was performed.
3. Results
3
.
1
. Dry matter accumulations of lea6es, bracts, and floral buds
When a square at a given branch position was 5 – 7 days old, the subtending sympodial leaf had
just unfolded. Thereafter, leaf DW increased rapidly with increasing square age Fig. 2A and
reached the greatest DW when the square at the corresponding position became a white flower.
During square development, the increase in bract DW of individual squares with square age
was similar to that of the subtending leaf Fig. 2B. The increase in floral bud DW with pro-
gressing square age exhibited a typical exponential growth pattern Fig. 2C. Floral bud DW in-
creased slowly during the first 15 days of square development. Thereafter, the bud DW increased
rapidly and tripled within the last 5 – 8 days of square development a 20-day-old square to a
white flower compared to a 20-day-old floral bud.
Final DWs of subtending leaves, bracts, and floral buds of squares at the same fruiting position
did not differ between the years Fig. 2A – C. However, the node, branch position, and square
age significantly P B 0.001 affected the increases in the DWs of leaves, bracts, and floral buds. The
growth rates of leaf DW, bract DW and bud DW decreased as the main-stem node number in-
creased up the plant and branch position in- creased away from the main stem. Node and
branch position had smaller effect on floral bud DW compared to the DWs of subtending leaves
and bracts.
3
.
2
. Non-structural carbohydrates in lea6es In 1994, hexose, sucrose, starch and TNC con-
tents in subtending leaves varied significantly with square age and branch position P B 0.001 –
0.0001, except for sucrose which did not differ among branch positions Fig. 3. Age and posi-
tion also had a significant P B 0.001 interaction
Fig. 3. Changes in non-structural carbohydrate concentrations in the subtending fruiting branch leaves FBL of the first
three fruiting positions at main-stem Node 10 during square development in 1994. The LSD values are for all combinations
of positions and square ages. Each data point is the mean of nine samples from three replications and three subsamples in
each replication.
Fig. 2. Changes in dry matter weight of: A subtending leaves; B bracts; and C floral buds of cotton squares at different
main-stem nodes and sympodial branch positions during the development in 1993 and 1994. Arrows indicate flowering. The
LSD values are for all combinations of nodes, positions, and square ages. Each data point is the mean of 15 leaves or 30
squares from three replications.
effect on leaf non-structural carbohydrate concen- trations. Starch was the predominant non-struc-
tural carbohydrate in the leaves during square development and accounted for 70 – 91 of the
TNC. Hexoses and sucrose accounted for about 7 – 19 and 3 – 16 of TNC concentration, respec-
tively. The hexoses in sympodial leaves at Branch Positions 1 and 2 reached a peak between 15 and
20 days after square appearance at those positions and then decreased until flowering. However, the
hexoses in the sympodial leaf at Branch Position 3 increased linearly during the square development
period and peaked at flowering. Although the sympodial leaf at Branch Position 2 had a higher
hexose concentration than the sympodial leaf at Position 1 throughout square development, the
difference between Positions 1 and 2 Fig. 3 was
not significant during hexose peak 15 – 20 days. Except for a drop at day 20, leaf sucrose con-
centration also showed a marked increase with increasing square age. Sucrose concentration in
the sympodial leaves was highest just prior to flowering 25-day-old squares Fig. 3. Leaf
starch concentration also rapidly increased with increased square age and peaked at 5 days before
flowering for the sympodial leaf at Branch Posi- tion 2 or at flowering for the sympodial leaves at
Branch Positions 1 and 3. Of the three sympodial leaves, the leaf at Branch Position 2 exhibited the
highest
concentrations of
starch and
TNC, whereas the leaf at Branch Position 1 had the
lowest carbohydrate concentrations at the same square age. Starch and TNC were significantly
different P B 0.05 between branch positions within the plant canopy Fig. 3 except for Posi-
tions 2 and 3 at 10-day square age and at flowering.
3
.
3
. Non-structural carbohydrates in bracts Square age, node and branch position signifi-
cantly P B 0.01 – 0.0001 affected contents of bract hexoses, sucrose, starch, and TNC. Interac-
tive effects on non-structural carbohydrates were also significant P B 0.001 – 0.0001 among age,
node, and position.
In 1993, the bract hexose concentration ranged between 4 and 8 g kg
− 1
DW, accounting for 11 – 15 of the TNC, and was relatively consistent
among square ages Fig. 4. The change over time in bract sucrose concentration showed a greater
range 2 – 15 g kg
− 1
DW and variation among sampling dates, nodes or branch positions, com-
pared to the bract hexoses. Overall, bract starch concentration accounted for 65 – 76 of the TNC
and slowly decreased with increasing square age except for Position 1 of Node 12. There were no
consistent differences in concentrations of bract
Fig. 4. Changes in non-structural carbohydrate concentrations in the bracts during the development of squares at different branch positions of main-stem Nodes 8, 10 and 12 in 1993, and sympodial Branch Positions 1, 2 and 3 of main-stem Node 10 in 1994. White
flower occurred at 25 days in 1993 and 28 days in 1994 after first visible appearance of the square. The LSD values are for all combinations of nodes, positions, and square ages. Each data point is the mean of nine samples from three replications and three
subsamples in each replication.
Fig. 5. Changes in non-structural carbohydrate concentrations in the floral buds during the development of squares at different branch positions of main-stem Nodes 8, 10 and 12 in 1993, and sympodial Branch Positions 1, 2 and 3 of main-stem Node 10 in
1994. White flower occurred at 25 days in 1993 and 28 days in 1994 after first visible appearance of the square. The LSD values are for all combinations of nodes, positions, and square ages. Each data point is the mean of nine samples from three replications
and three subsamples in each replication.
hexoses and sucrose between nodes and between branch positions during square development, but
averaged the first two branch positions of each node, bract starch and TNC concentrations of
squares at Node 8 were significantly higher than those on Nodes 10 and 12 at most sampling dates
in 1993.
In 1994, concentrations of hexoses, sucrose and starch in bracts were similar to those in 1993, but
their patterns changed over time differently be- tween the years Fig. 4. Similar to the leaf su-
crose, the bract sucrose concentration was more variable than hexoses and starch levels, and the
bracts of squares at Branch Position 1 showed the lowest concentrations of starch and TNC P B
0.05 among the three branch positions Positions 1, 2 and 3. This might be associated with the
shade of main-stem leaves in the upper canopy.
3
.
4
. Non-structural carbohydrates in floral buds In general, floral-bud non-structural carbohy-
drate concentrations averaged across all square ages were influenced significantly by node P B
0.01, branch position P B 0.001 and square age P B 0.0001, except for the starch and TNC in
1994 Fig. 5. There were significant P B 0.001 – 0.0001 node × branch position, node × age, posi-
tion × age, and node × position × age interaction effects on floral-bud hexose, sucrose, starch, and
TNC concentrations. Compared with subtending leaves and bracts, floral buds had the highest
hexoses and the lowest sucrose concentrations P B 0.05, but starch and TNC concentrations of
floral buds were higher than those of bracts and lower than those of subtending leaves Table 2.
The patterns of changes in the concentrations
of non-structural carbohydrates in floral buds during square development are shown in Fig. 5.
The hexose and sucrose concentrations in floral buds remained relatively constant between 5 and
25 days of square development. During this pe- riod, hexose concentration was 5 – 12 g kg
− 1
DW, and sucrose 2 – 6 g kg
− 1
DW. At anthesis, the floral-bud hexose concentration tripled in 1993
and more than quadrupled in 1994, compared to the floral-bud hexoses of 20-day-old squares. The
sucrose in floral buds was less than 10 g kg
− 1
DW before anthesis, and rose above 60 g kg
− 1
DW in 1993 and above 35 g kg
− 1
DW in 1994 means of squares at all positions. Starch concen-
tration was lowest in the buds of 10 – 15-day-old young squares 30 – 50 g kg
− 1
DW. Thereafter, floral-bud starch concentration rapidly increased
as square age increased, and reached the greatest values at anthesis. During square development,
there were no consistent differences in hexose and sucrose concentrations among the squares at the
different nodes and branch positions within a year. The squares at Branch Position 2 of Node
12 had the lowest floral-bud starch concentration during the first 15 days of square development in
1993. However, the buds at Branch Position 3 of Node 10 had the highest starch concentration
during the early period 5 and 10 days of square growth in 1994.
Averaged across all square ages and Branch Positions 1 and 2 of Node 10 by the years data
not shown found significant difference between years in floral-bud non-structural carbohydrate
concentrations. Floral buds in 1994 had higher hexoses, lower sucrose, higher starch and higher
TNC concentrations P B 0.05 than those in 1993. The differences in bud non-structural carbo-
hydrate concentrations between years were proba- bly associated with temperature during square
ontogeny. The heat units during square develop- ment in 1993 were greater than those in 1994
Table 1. Further study is needed for temperature effects on non-structural carbohydrate contents of
cotton tissues.
4. Discussion
