Environmental and Experimental Botany 43 2000 45 – 53
Effect of enhanced ultraviolet-B radiation on pollen germination and tube growth of 19 taxa in vitro
Huyuan Feng
a
, Lizhe An
a,b
, Lingling Tan
a
, Zongdong Hou
a
, Xunling Wang
a,c,
a
School of Life Science, State Key Laboratory of Arid Agrioecology, Lanzhou Uni6ersity, Lanzhou,
730000
, PR China
b
State Key Laboratory of Frozen Soil Engineering, Geocryology Lanzhou Institute of Glaciology and Geocryology, CAS. Lanzhou,
730000
, P.R. China
c
Department of Biology, Northwest Uni6ersity, Xi
’
an,
710069
, P.R. China Received 17 February 1999; received in revised form 1 September 1999; accepted 3 September 1999
Abstract
In order to determine the response of pollen to UV-B irradiation and cumulative effects of UV-B exposure time on pollen germination and tube growth, 19 taxa of higher plants were investigated in vitro concerning the exposure of
pollen grains to two levels of enhanced ultraviolet-B UV-BBE 280 – 320 nm, 350 and 500 mWm
2
biologically effective UV-B radiation simulating 8 and 21 stratospheric ozone depletion in Lanzhou, China 36.04°N, 1550 m
and to no UV-B control group. Compared with the control, enhanced UV-B radiation significantly inhibited pollen germination and tube growth in most species. Higher UV-B flux rate caused a greater inhibitory effect than lower
UV-B radiation level. Several taxa exhibited insensitivity of pollen germination and tube growth to UV-B and were even stimulated by UV-B. Reduction in pollen germination rates and tube growth increased with longer exposure time
and this indicated a cumulative effect of UV-B radiation. It is concluded that changes in pollen susceptibility to UV-B would lead to severe ecological consequences under natural conditions. © 2000 Elsevier Science B.V. All rights
reserved.
Keywords
:
Pollen germination; Pollen tube growth; Ultraviolet-B UV-B radiation www.elsevier.comlocateenvexpbot
1. Introduction
Anthropogenic emissions of chloroflorocarbons CFCs and nitrogen oxides result in depletion of
the stratospheric ozone layer, which protects life on earth against deleterious short-wave solar radi-
ation. As a result, the amount of biologically effective UV-B irradiance UV-BBE reaching the
earth’s surface increases Kerr, 1993. Recent mathematical models predict a further increase in
solar UV-B radiation Madronich et al., 1995. Recently an ‘ozone hole’ has been discovered
above the Qinghai-Tibet Plateau in China Zhou et al., 1995.
Corresponding author. E-mail address
:
fenghylzu.edu.cn X. Wang 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 4 2 - 8
Since Johnston 1971 first reported the poten- tial stratospheric ozone reduction over two
decades ago, UV-B effects on higher plants have been the subject of considerable research Cald-
well et al., 1995. A wide range of biochemical, physiological,
morphological, anatomical
and growth responses have been extensively investi-
gated, but little is known about UV-B effect on reproductive biology Demchik and Day, 1996;
Van de Staaij et al., 1997; Torabinejad et al., 1998. In some species an effect of elevated UV-B
radiation on total plant seed production has been found Van de Staaij et al., 1997. Although pol-
len of open flowers appears to be well shielded from solar UV-B when still within the anther sacs
Flint and Caldwell, 1983, it may be exposed to natural UV-B radiation following dehiscence until
successful germination and stigma penetration oc- cur. The exposure time of individual pollen tubes
to natural UV-B flux rates depends on the time required for individual pollen tube to grow from
the germinated pollen grains up to penetration of stigma. This time in vivo varies considerably
among species and pollen grain types, averaging 13 – 57 min summarized by Torabinejad et al.,
1998. Moreover, pollen grain walls can transmit as much as 20 of the UV-B Stadler and Uber,
1942, therefore, most of the studies concerning UV-B effects on reproductive characteristics of
higher plants have been focused on pollen.
Pollen germination and tube elongation in most species or cultivars are inhibited by enhanced
UV-B radiation in vitro. For instance, Flint and Caldwell 1984 reported partial inhibition of in
vitro pollen germination in Scrophularia pere- grina, Geranium 6iscosissimum, Papa6er rhoeas,
and Cleome lutea under elevated UV-B radiation. Musil 1995 reported reduced pollen germination
in two out of eight species tested. Decrease of in vitro pollen tube growth under UV-B has been
observed for Nicotiana tabacum and Petunia hy- brida Feder and Shrier, 1990. For four dicotyle-
donous Asteraceae and four monocotyledonous Iridaceae tested, pollen tube growth of all di-
cotyledonous species and one Iridaceae species was reduced Musil, 1995. In a recent report,
Torabinejad et al. 1998 detected differences among 34 species under two levels of UV-B expo-
sure to in vitro pollen grains, and found that the length of pollen tube of more than 50 of the
taxa tested was significantly reduced and the pol- len germination of five taxa was significantly in-
hibited. In comparison with other physiological andor ecological effects of enhanced UV-B irra-
diance, less than 70 species or cultivars of higher plants have been examined regarding the effect of
elevated UV-B on pollen. More studies in this field are obviously necessary to gain a better
understanding of the effect of increased UV-B radiation.
Previous research has often been conducted un- der low levels or in the absence of visible light.
This prohibits the process of photorepair of the UV-B induced damage to the DNA Pang and
Hays, 1991. Therefore a radiation regime in which UV-B radiation was combined with suffi-
ciently visible light was used in this experiment.
At present it is not clear whether UV-B damage accumulates over time. Zea mays Pfahler, 1973,
Brassica rapa Demchik and Day, 1996 and Di- morphotheca sinuata Musil, 1996 only have been
studied. In the present study we subjected mature pollen from 19 plant taxa to different UV-B
regimes to determine: i the interspecific response of pollen germination and tube elongation in vitro
to enhanced UV-B radiation, and ii whether there was a cumulative effect of UV-B exposure
duration on pollen germination and tube growth. Here we hypothesize that the cumulative effect of
UV-B over time exists and that as a consequence, pollen germination and tube elongation under
longer exposure to UV-B will be inhibited more seriously than under shorter exposure time.
2. Material and methods
