Environmental and Experimental Botany 43 2000 185 – 195
Dynamics of non-structural carbohydrates in developing leaves, bracts and floral buds of cotton
D. Zhao , D.M. Oosterhuis
Department of Crop, Soil, and En6ironmental Sciences, Altheimer Laboratory,
276
Altheimer Dri6e, Uni6ersity of Arkansas, Fayette6ille, AR
72704
, USA Received 29 July 1999; received in revised form 22 October 1999; accepted 26 October 1999
Abstract
Development of cotton Gossypium hirsutum L. squares i.e. floral buds with bracts is fundamental for yield formation. A 2-year field study was conducted to determine dry weight DW accumulations of cotton leaves, floral
bracts and floral buds, and the changes in concentrations of non-structural carbohydrates hexoses, sucrose and starch in these tissues during square ontogeny as affected by fruiting positions within the plant canopy. During
square development, DW accumulation of a subtending sympodial leaf and floral bracts followed a sigmoid growth curve with increasing square age, whereas the DW increase of a floral bud followed an exponential curve. Main-stem
node Node 8, 10 or 12 and branch position proximal vs. distal within a plant canopy significantly affected DW accumulations of the leaf, bracts and floral bud. Starch was the dominant non-structural carbohydrate in the three
tissues, accounting for more than 65 of total non-structural carbohydrates TNC. Subtending leaf TNC increased as square age increased. The bracts exhibited a smaller change in TNC than leaves. Non-structural carbohydrate
concentration was the lowest in 10-day-old floral buds, and had little change during the first 15 days of square development. Within 5 days prior to anthesis, the floral-bud TNC increased dramatically, tripling at the time of floral
anthesis compared with 15-day-old floral buds. Square age and fruiting position significantly affected non-structural carbohydrate concentrations of subtending leaves, bracts, and floral buds. The correlation did not exist between final
boll retention and non-structural carbohydrate concentrations of floral buds at different fruiting positions under normal growth conditions. The pattern of floral-bud non-structural carbohydrates during square ontogeny suggests
that major events in carbohydrate metabolism occur just prior to anthesis. © 2000 Elsevier Science B.V. All rights reserved.
Keywords
:
Gossypium hirsutum; Floral bud development; Dry matter accumulation; Hexoses; Sucrose; Starch concentration www.elsevier.comlocateenvexpbot
1. Introduction
Yield of field-grown cotton is closely associated with the number of mature bolls Wells and
Meredith, 1984; Heitholt, 1993. The number of bolls per unit land area is partially dependent on
Corresponding author. Tel.: + 1-501-575-3955; fax: + 1- 501-575-3975.
E-mail address
:
dzhaocomp.uark.edu D. Zhao S0098-847200 - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 0 9 8 - 8 4 7 2 9 9 0 0 0 5 9 - 3
the number of squares floral buds with bracts retained by the plants. Therefore, a better under-
standing of the initiation, differentiation and devel- opment of cotton squares, and the characteristics
of their physiology and biochemistry during devel- opment are important for improving cotton man-
agement.
The development of cotton squares is a funda- mental step of fruit development. However, most
studies on squares have emphasized the relation between morphology and abscission McMichael
and Guinn, 1980; Ungar et al., 1989. We know much less about the physiology of square forma-
tion and growth than any other part of the cotton fruiting cycle Stewart, 1986. Since only limited
studies have been carried out on the physiology of square development, there are many phenomena
and questions about cotton fruit development that are not completely understood. For instance, why
do cotton plants shed young squares and young bolls, but not white flowers? Why is the abscission
of small squares greater than that of large squares? How do the carbohydrate and mineral nutrient
profiles of squares change during development? Are there differences in carbohydrate concentrations in
floral buds and bracts located at different fruiting positions?
The endogenous hormone balance, photosyn- thetic assimilate supply, and mineral nutrient status
of plants are major physiological factors con- trolling fruit abscission Benedict, 1984. Environ-
mental factors inducing fruit abscission include adverse photosynthetic photon flux density, tem-
perature, moisture, and nutrition Guinn, 1974, 1982. McMichael and Guinn 1980 suggested that
the sensitivity of cotton square abscission to water stress was greatest during the first week after the
squares become visible. Later studies showed that squares smaller than 1 cm in size were more
sensitive to stress environments inducing abscission than the squares larger than 1 cm in size Guinn,
1982; Ungar et al., 1989.
Development of young squares into flowers is an important process of yield development. However,
squares often fail to form flowers. If this failure occurs with too many squares abscised, crop yield
can be reduced and maturity can be delayed. The hypothesis of this study is that the non-structural
carbohydrate contents of floral buds may be used to explain the differences in the boll retention at
different main-stem nodes and fruiting positions. Since the physiological reasons for that failure are
not well understood and because there is little information on this topic, the objective of this
research was to characterize leaf and square carbo- hydrate concentrations as a function of square age,
sympodial branch position i.e. proximal vs. distal and vertical main-stem node i.e. Node 8, 10 or 12
within the canopy.
2. Materials and methods
