Hah. Graham et Dr. Decoteau, YOUNG WATERMELON PLANT-GROWTH RESPONSES TO END-OF-DAY RED AND FAR-REDLIGHT ARE AFFECTED BY DIRECTION OF EXPOSURE AND PLANT-PART EXPOSED, Scientia horticulturae, 69(1-2), 1997, pp. 41-49
Differences in the growth regulating ability of end-of-day (EOD) red (
R) and far-red light (FR) as affected by direction of exposure (predom
inantly downwardly versus upwardly directed) and plant part exposed (a
daxial and abaxial surface of leaf 1, and junction and opposite the ju
nction of the attachment of the petiole to the stem) were determined o
n young watermelon (Citrullus lanatus (Thumb.) Matsum and Naki cv. Sug
ar Baby) seedlings in a controlled environment. Whole-plant exposure t
o downwardly or upwardly directed EOD FR stimulated elongation of inte
rnode 1 and the petiole of leaf 1 (as measured from the cotyledons) as
compared to control seedlings (no EOD light). Upwardly directed EOD F
R also induced elongation of internode 2, stem length, and leaf petiol
es 2 and 3 as compared to controls. This EOD FR induced elongation was
reversed by following the FR with a red light treatment (FR + R) impl
icating phytochrome regulation. Upwardly directed EOD FR increased the
leaf angle of leaf I as compared to controls. Upwardly directed EOD R
and EOD FR + R increased the petiole angle of leaf 1. Irradiation of
the adaxial surface of leaf 1 with fibre-optic transmitted EOD FR (tis
sue area exposed approximately equal to 20cm(2)) enhanced elongation o
f internode 1 by 88% as compared to controls. Irradiation of the abaxi
al surface of leaf 1 and the junction and side opposite the junction o
f the point of attachment of petiole 1 to the stem with EOD light had
no effect on elongation of internodes 1 and 2 or stem length. In concl
usion, the growth regulating ability of photomorphogenic light (as pro
vided by EOD R and FR) was affected by predominant direction of exposu
re.