Mycorrhizal impact on drought stress tolerance of rose plants probed by chlorophyll a fluorescence, proline content and visual scoring |
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Authors: | Alexandra Pinior Gisela Grunewaldt-Stöcker Henning von Alten Reto J Strasser |
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Institution: | Institute of Plant Diseases and Plant Protection, University of Hannover, Germany. |
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Abstract: | Micropropagated rose plants (Rosa hybrida L., cv. New Dawn) were inoculated with the arbuscular mycorrhizal (AM) fungus Glomus intraradices (Schenk and Smith) and subjected to different drought regimens. The dual objectives of these experiments were to investigate
the mechanism and the extent to which AM can prevent drought damages and whether physiological analyses reveal enhanced drought
tolerance of an economically important plant such as the rose. In a long-term drought experiment with four different water
regimens, visual scoring of wilt symptoms affirmed that AM in a selected host–symbiont combination increased plant performance.
This effect was mostly expressed if moderate drought stress was constantly applied over a long period. In a short-term experiment
in which severe drought stress was implemented and plants were allowed to recover after 4 or 9 days, no visual differences
between mycorrhizal and non-mycorrhizal roses were observed. Therefore, the early physiological steps conferring drought tolerance
were prone to investigation. Proline content in leaves proved to be an unsuitable marker for AM-induced drought tolerance,
whereas analysis of chlorophyll a fluorescence using the JIP test (collecting stress-induced changes of the polyphasic O-J-I-P fluorescence kinetics in a non-destructive
tissue screening) was more explanatory. Parameters derived from this test could describe the extent of foliar stress response
and help to differentiate physiological mechanisms of stress tolerance. AM led to a more intense electron flow and a higher
productive photosynthetic activity at several sites of the photosynthetic electron transport chain. A K step, known as a stress
indicator of general character, appeared in the fluorescence transient only in drought-stressed non-mycorrhizal plants; conversely,
the data elucidate a stabilising effect of AM on the oxygen-evolving complex at the donor site of photosystem (PS) II and
at the electron-transport chain between PS II and PS I. If drought stress intensity was reduced by a prolonged and milder
drying phase, these significant tolerance features were less pronounced or missing, indicating a possible threshold level
for mycorrhizal tolerance induction. |
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Keywords: | Arbuscular mycorrhiza Chlorophyll fluorescence Drought stress tolerance Glomus intraradices Rosa hybrida |
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