A Database for Triticeae and Avena
II.18. Effects of kinetin on photosynthesis and growth response of
R. G. McDaniel. Department of Agronomy and Plant Genetics, University
of Arizona, Tucson, Arizona 85721, U.S.A.
Photosynthetic rates of barley trisomics have been found to be inferior
to those of normal diploids (McDaniel, BGN 1:29, 1971). Phenotypic characteristics
of barley plants having extra chromosomes 1 and 2 resembled those of plants
characterized by hormonal imbalances. Trisomics 1 or 2, under appropriate
environmental conditions, exhibit aerial roots and epinasty, characteristic
of high auxin concentration (Imber and Tal, Science 169:592, 1970). Additionally,
leaves of these trisomics unroll slowly, and are more narrow than those
of normal diploids; these effects may relate to cytokinin concentration
in leaves. I tested this hypothesis by watering trisomics with exogenous
kinetin (10-6 M) and observing physiological and biochemical
responses after 24 hours.
Kinetin affected both degree of leaf unrolling and rate of leaf expansion
of plants trisomic for chromosome 1 or 2. These effects could be noted
within 4 hours on treated trisomics: observations were then continued for
at least 3 days. No significant response of leaf morphology was noted in
the kinetin-treated diploid. These data are summarized in Table 1.
Table 1. Width of young leaves (in mm) of kinetin-treated
(K) trisomics and diploids of Hordeum vulgare L. cv. 'Betzes'.
Young leaves of barley trisomics 1 or 2 present a somewhat triangular
cross-section. This is most noticeable in leaves of trisomic 1, which remain
tightly "rolled under a variety of photoperiods and light intensities.
Kinetin treatment causes a rapid "unrolling" of leaves of these trisomics.
This serves as an easily monitored physiological response to kinetin and
resembles the growth regulation-controlled leaf unrolling effects previously
described (Poulson and Beevers, Plant Physiol. 46:509, 1970; Beevers, et
al. Planta 90:286, 1970).
Effects of exogenous kinetin on plant photosynthetic rates have been
described (Wareing, et al. Nature 220:453, 1968; Meidner, J. Exptl. Bot.
18:556, 1967). These experiments have pointed out the relation between
cytokinin concentration and rate of protein synthesis in young leaves.
The inferior photosynthetic rates I previously observed with barley trisomics
prompted me to examine the possible effects of kinetin on barley leaf photosynthetic
rates. Data indicated that kinetin treatment elicited a marked increase
(27%) in photosynthetic rates of these trisomics. as illustrated in Table
2. Plants trisomic for chromosome 1 gave a similar response.
Table 2. Photosynthesis of leaf disks of kinetin-treated
trisomics and diploids of barley. Data are presented in mu liters
O2 evolution per leaf disk per hour at 25°C + the
standard error of three experiments, three replications. (See McDaniel,
BGN 1:29, 1971, for methods).
Photosynthetic rates of kinetin-treated trisomics greatly exceeded that
of untreated trisomics, and approached the rates of the diploids, expressed
on an area, unit protein or unit chlorophyll basis. Kinetin treatment also
appeared to increase dark respiration of trisomics, although significance
has not been established. Photosynthetic measurements using attached leaves
monitored in a closed system by I. R. spectrophotometry have verified the
data of Table 2 (McDaniel, unpublished). Kinetin treatment also increased
the transpiration rate of the trisomics. These and other physiological
responses of trisomics to hormone treatment, including stomatal response
(Pailas and Box, Nature 227:87, 1970) and senescence (Adedipe et al., Physiol.
Plant 25:151, 1971) are presently being investigated. The experiments reported
here indicate that barley trisomics are excellent systems for biochemical
studies on hormonal plant growth regulation.
BGN 2 toc
BGN Main Index