Temperature-dependent alterations of respiration in leaves of two selected vascular plant species: the role of the alternative oxidase pathway

Alterações de respiração dependentes de temperatura em folhas de duas espécies de plantas vasculares selecionadas: o papel do caminhamento alternativo da oxidase

BOTANY AND PLANT PHYSIOLOGY

NOTE

Temperature-dependent alterations of respiration in leaves of two selected vascular plant species: the role of the alternative oxidase pathway

Alterações de respiração dependentes de temperatura em folhas de duas espécies de plantas vasculares selecionadas: o papel do caminhamento alternativo da oxidase

Natalia V. Pystina; Roman A. Danilov

Department of Natural & Environmental Sciences, Mid Sweden University, S-87188 Härnösand, Sweden. E-mail: [e-mail]

ABSTRACT

Effects of higher temperatures on respiration and activity of alternative oxidase (AOX) were studied in mature leaves of Ajuga reptans L. and Rhodiola rosea L. Total respiration in both A. reptans and R. rosea increased exponentially with the increasing temperature of 10 °C to 35 °C. Respiration in the presence of benzhydroxamic acid (BHAM) also increased exponentially in accordance with the increasing temperature in the leaves of both A. reptans and R. rosea. Relative activity of the alternative pathway decreased significantly in the leaves of A. reptans with increasing temperatures. However, an increase in the relative activity of the alternative pathway was detected in the leaves of R. rosea. Thermoresistance of the alternative respiratory pathway was considered to be higher in R. rosea compared to A. reptans. We suppose that A. reptans and R. rosea have different mechanisms regulating partitioning of electrons to the alternative respiratory pathway.

Key words: alternative respiratory pathway, respiration, alternative oxidase, leaves, temperature.

RESUMO

Estudaram-se os efeitos de temperaturas mais altas na respiração e na atividade do caminhamento alternativo da oxidase (AOX) em folhas maduras de Ajuga reptans L. e de Rhodiola rosea L. Verificou-se que a respiração total, tanto em A. reptans como em R. rosea, apresentou aumento exponencial com a temperatura crescente de 10 ºC para 35 ºC. Observou-se, também, que na presença de ácido benzidroxâmico (BHAM) houve aumento exponencial na respiração com a variação crescente da temperatura nas folhas das duas plantas estudadas. A atividade relativa do caminhamento alternativo diminuiu significativamente nas folhas de A. reptans com temperaturas crescentes; verificou-se, porém, aumento nas folhas de R. rosea. A termorresistência do caminhamento respiratório alternativo foi considerada mais alta em R. rosea que em A. reptans. Supõe-se que ambas possuem diferentes mecanismos que regulam a partição de elétrons para o caminhamento respiratório alternativo.

Palavras-chaves: caminhamento respiratório alternativo, respiração, oxidase alternativo, folhas, temperatura.

Temperature is considered to be one of the most important environmental factors affecting all physiological processes in plants. Respiration is one of the key processes in plants providing them with energy and metabolites. General relations between temperature and respiration are well known (LARCHER, 1995). However, reports on the influence of temperature on the alternative respiratory pathway in vascular plants are really scarce (VANLERBERGHE and MCINTOSH, 1997). A cytochrome pathway (cyanide-sensitive) and an alternative pathway (cyanide-resistant) are considered to be principal parts of the respiratory chain in plant mitochondria. The alternative pathway consists of only one enzyme – alternative oxidase (AOX) and is generally considered to be nonphosphorylating (e.g. MCINTOSH, 1994). There are some evidences that the alternative pathway plays a role in thermogenesis in aroids and other species (MEEUSE, 1975). However, the role of AOX in non-thermogenic tissues of vascular plants remains still unclear (WAGNER and KRAB, 1995). As stated by numerous authors, alternative pathway is an important feature of respiration in plants and, therefore, new evidences contributing to our knowledge of regulatory mechanisms of the alternative pathway are urgently needed (for an excellent review see VANLERBERGHE and MCINTOSH, 1997).

There are some reports in the literature dealing with influence of low temperatures on the AOX activity (VANLERBERGHE and MCINTOSH, 1997, GONZALEZ-MELER et al., 1999). On the other hand, knowledge of effects of increasing temperature on AOX activity under natural conditions is of a particular interest. We studied how activity of AOX depends on increasing temperature in mature leaves of Ajuga reptans L. and Rhodiola rosea L. – two common species in natural plant communities in Komi Republic, Russia. A. reptans was chosen as the study object because it is a common shade-enduring habitant in European natural forest communities. We have investigated A. reptans from their northern areal. In this area A. reptans is one of the few postglacial relicts. R. rosea has its importance as well-known medical plant. The choice of R. rosea was justified by pure knowledge of temperature-mediated effects on this important medical plants.

Material and Methods

All experiments with both A. reptans and R. rosea were carried out under natural conditions with sufficient light supply near Syktyvkar (62° 52' N), northeast Russia. Only mature (July) leaves of A. reptans and R. rosea were investigated. The leaves were continuously sampled from 15 plants at 9.00 a.m. in order to avoid any possible artefacts caused by photosynthesis metabolites.

Small pieces (0.0028 dm²) were cut off from sampled leaves (three pieces per leave). The pieces were placed in a cuvette and the respiration was estimated by oxygen consumption (mmol O₂ g^-1FW h^-1) with the aid of an electrode of Clark-type at following temperatures: 10°, 20°, 25° and 35° C. Activity of the alternative respiratory pathway (v_alt) was studied using method of specific inhibitors (BAHR and BONNER, 1973; THEOLOGIS and LATIES, 1978) and was estimated as the difference between total respiration (without inhibitors) and respiration in the presence of benzhydroxamic acid (BHAM, 25.0 mmol). All experiments were carried out in triplicate.

Statistical analyses were performed in the computer package Minitab 13.0.

Results and Discussion

Total respiration in the mature leaves of both A. reptans and R. rosea increased exponentially with the increasing temperature of 10 °C to 35 °C (Fig. 1). By increase in temperature, temperature coefficient (Q₁₀) decreased from 2.2. to 1.5 in the leaves of A. reptans and from 2.2 to 1.6 in the leaves of R. rosea. Exponential behaviour of the respiration curves obtained can be considered as an evidence of a general absence of a profound stress in A. reptans and R. rosea in the temperature range studied (CRIDDLE et al., 1997). These facts correspond well with the actual knowledge concerning general dependence of respiration on temperature (e.g. Larcher, 1995). Respiration in the presence of BHAM also increased exponentially in accordance with the increasing temperature in the leaves of both A. reptans and R. rosea. Consequently, this phenomenon can be mainly explained by the activation of the cytochrome respiratory pathway which is resistant to BHAM.

Relative activity of the alternative pathway decreased significantly in the leaves of A. reptans with increasing temperatures. However, an increase in the relative activity of the alternative pathway was detected in the leaves of R. rosea (Tab. 1). We suppose that A. reptans and R. rosea have different mechanisms regulating partitioning of electrons to the alternative respiratory pathway. Previous studies showed a general increase in AOX protein concentration and activity of the alternative pathway in plant tissues at lower temperatures (VANLERBERGHE and MCINTOSH, 1992; ITO et al., 1997). However, data on the influence of higher temperature on the activity of AOX are more than scarce. A decline in the sensitivity of respiration to inhibitors of AOX was reported in the temperature range of 35-45 °C (Chauveau et al., 1978). GONZALEZ-MELER et al. (1999) reported an increase in the activities of both main and alternative pathway respiration at increasing temperatures up to 35 °C. Our results show that the sensitivity of respiration to the inhibitor of AOX (BHAM) increased exponentially according to the enhancing temperatures in both A. reptans and R. rosea. This phenomenon is controversial to that reported by Chauveau et al. (1978). However, the relative partitioning of electrons to the alternative pathway decreased in the leaves of A. reptans and increased in the leaves of R. rosea when temperatures increased.

The role of AOX in vascular plants is still under debate (VANLERBERGHE and MCINTOSH, 1997). It is being discussed if the alternative respiratory pathway can act as one of the important mechanisms acting by chilling acclimatisation (e.g. MOYNIHAN et al., 1995). However, there is currently no reasonable hypothesis dealing with effects of higher temperatures on the activity of AOX. Our results let us postulate thermolability of respiration at higher temperature in two species studied. Partitioning of electrons to the alternative pathway seems to be considerably varying both in A. reptans and R. rosea. We suppose that the alternative respiratory pathway is more thermoresistant in R. rosea compared to A. reptans. However, our results do not allow any reasonable speculations concerning a possible role of the alternative respiratory pathway at higher temperatures in the species studied.

Conclusions

Total respiration in mature leaves of both A. reptans and R. rosea increased exponentially with the increasing temperature of 10 °C to 35 °C. With increasing temperatures, relative activity of the alternative pathway decreased significantly in the leaves of A. reptans while increased in the leaves of R. rosea. Thermoresistance of the alternative respiratory pathway can be considered to be higher in R. rosea compared to A. reptans. Different mechanisms regulating partitioning of electrons to the alternative respiratory pathway can be a valuable explanation to the phenomena detected.

Received for publication in August 27, 2001, and approved in May 9, 2002

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Publication Dates

• Publication in this collection
  16 Feb 2004
• Date of issue
  Aug 2002

History

• Received
  27 Aug 2001
• Accepted
  09 May 2002