Climatic factors influence leaf structure and thereby affect the ozone
sensitivity of Ipomoea nil ‘Scarlet O'Hara’
B
arbara B. Moura
*
, Edenise S. Alves
Instituto de Bot^ anica, Caixa Postal 3005, 01061-970 S~ ao Paulo, SP, Brazil
article info
Article history:
Received 30 April 2014
Received in revised form
25 June 2014
Accepted 27 June 2014
Available online
Keywords:
Air pollution
Bioindicator
Tropical environment
S~ ao Paulo
Brazil
abstract
Phenotypic plasticity of the leaves can interfere with the plant sensitivity to ozone (O
3
) toxic effect. This
study aimed to assess whether the leaf structure of Ipomoea nil changes due to climatic variations and
whether these changes affect the species' sensitivity. Field exposures, in different seasons (winter and
spring) were made. The leaves that developed during the winter were thinner, with a lower proportion of
photosynthetic tissues, higher proportion of intercellular spaces and lower density and stomatal index
compared to those developed during the spring. The temperature and relative humidity positively
influenced the leaf thickness and stomatal index. The visible injuries during winter were positively
correlated with the palisade parenchyma thickness and negatively correlated with the percentage of
spongy parenchyma; during the spring, the symptoms were positively correlated with the stomatal
density. In conclusion, the leaf structure of I. nil varied among the seasons, interfering in its sensitivity
to O
3
.
© 2014 Elsevier Ltd. All rights reserved.
1. Introduction
The Metropolitan Region of S~ ao Paulo city (MRSP) is composed
of 39 cities with a population of approximately 20 million habitants
representing 75% of the population of S~ ao Paulo State. There are 8.5
million vehicles in this area, which contribute to high emission
levels of primary pollutants in the air as a result of fuel combustion.
As a result of complex photochemical reactions, ozone (O
3
) is
formed throughout the year in tropical environments (Moura et al.,
2014b). O
3
is considered a powerful phytotoxic pollutant that can
cause oxidative stress to vegetation, leading to the development of
specific visible injury in the leaves due to reactive oxygen species
(ROS), which react with lipids membranes (Schraudner et al., 1998),
inducing a type of programmed cell death known as
hypersensitive-like reaction (HR-like, Vollenweider et al., 2003;
2013; Moura et al., 2014a).
An extended and integrated assessment of environmental in-
dicators for global change is one of the most important emerging
research field (Serengil et al., 2011) and biomonitoring programs
are an efficient alternative consistently for monitoring the levels of
O
3
once the exposure is made following a standardized method
during a time series using specific sensitive species (Klumpp et al.,
2001).
The intimate relation between the leaf structure and its physi-
ological role has been discussed for a long time (Toth, 1982;
Roderick et al., 1999). Within different populations of the same
species, functional leaf traits may vary in relation to the extent that
the plant succeeds in acclimating to ambient oxidative pressure
(Bussotti, 2008). Higher palisade cell density and the greater
spongy mesophyll intercellular space may result in a larger amount
of free cell surface able to interact with O
3
(Bennet et al., 1992).
Relatively large substomatal chambers and abundant intercellular
spaces are anatomical features that reduce the resistance of leaves
to gas exchange and therefore favor O
3
diffusion within the leaves
(Calatayud et al., 2011).
One of the most interesting endogenous differences that may
lead to O
3
exposure sensitivity is stomatal density (Paoletti and
Grulke, 2005). Stomatal distribution and behavior respond to a
wide range of environmental stimuli such as light, humidity, and
CO
2
(Paoletti and Grulke, 2005). Stomatal responses to air pollut-
ants vary among species, leaf and tree age, and in conjunction with
other environmental stressors (Mansfield, 1998; Robinson et al.,
1998). Differences in stomatal density can also be correlate with
differences in the O
3
sensitivity of genotypes of the same species
(Ferdinand et al., 2000).
Ipomoea nil ‘Scarlet O'Hara’is an O
3
-sensitive species (Nouchi
and Aoki, 1979) that had been tested in tropical and subtropical
environments (Moura et al., 2011; Ferreira et al., 2012). However,
the efficiency of I. nil ‘Scarlet O'Hara’ for quantitative O
3
* Corresponding author.
E-mail addresses: bmourabio@gmail.com, bmourabio@yahoo.com (B.B. Moura).
Contents lists available at ScienceDirect
Environmental Pollution
journal homepage: www.elsevier.com/locate/envpol
http://dx.doi.org/10.1016/j.envpol.2014.06.042
0269-7491/© 2014 Elsevier Ltd. All rights reserved.
Environmental Pollution 194 (2014) 11e16