UV-B Radiation Affects Photosynthesis-Related Processes of Two Italian Olea europaea (L.) Varieties Differently.

Chiara Piccini,Maria Celeste Dias,Claudio Cantini,Roberta Longo,Marco Romi,Giampiero Cai

doi:10.3390/plants9121712

Chiara Piccini, Maria Celeste Dias + Show 4 more

Open Access

https://doi.org/10.3390/plants9121712

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Abstract

Given the economical importance of the olive tree it is essential to study its responses to stress agents such as excessive UV-B radiation, to understand the defense mechanisms and to identify the varieties that are able to cope with it. In the light of the analysis carried out in this study, we argue that UV-B radiation represents a dangerous source of stress for the olive tree, especially in the current increasingly changing environmental conditions. Both the varieties considered (Giarraffa and Olivastra Seggianese), although resistant to the strong treatment to which they were exposed, showed, albeit in different ways and at different times, evident effects. The two varieties have different response times and the Giarraffa variety seems better suited to prolonged UV-B stress, possible due to a more efficient and quick activation of the antioxidant response (e.g., flavonoids use to counteract reactive oxygen species) and because of its capacity to maintain the photosynthetic efficiency as well as a relatively higher content of mannitol. Moreover, pigments reduction after a long period of UV-B exposure can also be an adaptation mechanism triggered by Giarraffa to reduce energy absorption under UV-B stress. Olivastra Seggianese seems less suited to overcome UV-B stress for a long period (e.g., higher reduction of Fv/Fm) and has a higher requirement for sugars (e.g., glucose) possible to counteract stress and to restore energy.

Highlights

One of the issues intricately linked to climate change is the reduction of the ozone layer, the latter being significantly increased by air pollution [1]
Concerning the content of fructose, we found that fluctuations for the Olivastra Seggianese variety were statistically significant while those for the Giarraffa variety were not; at time point 2 the levels of this sugar in UV-B plants of both varieties were higher than in control plants (Figure 6B)
Given the high and multiple importance of the olive tree, it is essential to study its responses to stressful agents, such as excessive UV-B radiation, in order to understand the defense mechanisms and identify the most resistant varieties

Summary

Introduction

One of the issues intricately linked to climate change is the reduction of the ozone layer, the latter being significantly increased by air pollution [1]. The stratospheric ozone shields 90% of UV-B radiation [2], its degradation causes a higher exposure of organisms to this radiation and increases the risks connected to UV-B exposure [3]. The awareness of the dangerous effects of ozone layer reduction gave rise to several changes at the global level (e.g., implementation of the Montreal Protocol) resulting in the slowdown of the ozone layer depletion, but ozone layer is still lower than in the pre-1980 era. The levels of UV-B reaching the earth surface vary considerably, reaching values around 15 KJ m−2 d−1 in the Mediterranean basin or even extremely higher values, around 65 KJ m−2 d−1 , in Lhasa (Tibet) during the summer [5].

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