# The OJIP Kinetics Analysis Reveals Differential Thermal Tolerance Responses in Photosystem II of Coffea canephora Clones After Two Recurrent Cycles of Water Deficit

## TL;DR

This study shows that repeated drought stress in coffee plants can lead to heat tolerance in some clones but increased sensitivity in others.

## Contribution

The study reveals differential thermal tolerance responses in Coffea canephora clones after recurrent water deficit cycles.

## Key findings

- Clone 'A1' showed increased heat tolerance after drought cycles, while clone '3V' became more sensitive.
- High temperatures disrupted photosystem II function, as indicated by changes in OJIP kinetics and JIPTest parameters.
- Energy dissipation increased at 50 °C and 55 °C, affecting electron transport chain efficiency.

## Abstract

Coffea canephora cultivation areas in Brazil are frequently exposed to successive cycles of water deficit, triggering plant stress responses. In addition to water deficit, increased air temperature can act as a second stress factor. The recurrence of these stress factors may induce plant tolerance mechanisms, potentially mitigating future stress responses even of a different stress nature. We hypothesized that repeated cycles of water deficit can trigger tolerance mechanisms that make C. canephora leaves more resilient to supra-optimal temperatures. To test this hypothesis, young C. canephora plants were grown under non-limited water conditions for seven months (ΨmSoil > −20 kPa), after which they were subjected to two consecutive cycles of water deficit (ΨmSoil < −300 kPa), followed by rehydration. Two clones were used, ‘A1’ and ‘3V’, previously classified as drought sensitive and tolerant, respectively, considering the dynamics of physiological and architectural responses. After the second cycle, leaf discs were collected from completely expanded leaves formed during the two stress cycles and exposed to heat treatments (35 °C, 40 °C, 45 °C, 50 °C, and 55 °C) for 15 min in a water bath. Chlorophyll a fluorescence emission was then monitored, and the results were analyzed using OJIP transient kinetics and the JIPTest. High temperatures induced negative changes in both OJIP kinetics and JIPTest-derived parameters. A significant increase in F0 and a reduction in FM were observed mainly at 50 °C and 55 °C, due to changes in the stages of the OJIP curve. These changes impacted the “energy connectivity” and consequently the electron transport along the electron transfer chain (ETC), increasing energy dissipation, as confirmed by the JIPTest variables. Despite the high temperature impacts, previous water deficit induced heat tolerance in clone ‘A1’, while it increased sensitivity in clone ‘3V’. This study suggests that selecting drought-resistant varieties should consider their subsequent response to short high-temperature stress to avoid cross-sensitivity caused by selecting for a single environmental factor.