Halophytes, plants that survive to reproduce in environments where the salt concentration is around 200 mM NaCl or more, constitute about 1% of the worlds flora. Some halophytes show optimal growth in saline conditions; others grow optimally in the absence of salt. However, the tolerance of all halophytes to salinity relies on controlled uptake and compartmentalization of Na+, K+ and Cl- and the synthesis of organic compatible solutes, even where salt glands are operative. Although there is evidence that different species may utilize different transporters in their accumulation of Na+, in general little is known of the proteins and regulatory networks involved. Consequently, it is not yet possible to assign molecular mechanisms to apparent differences in rates of Na+ and Cl- uptake, in root-to-shoot transport (xylem loading and retrieval), or in net selectivity for K+ over Na+. At the cellular level, H+-ATPases in the plasma membrane and tonoplast, as well as the tonoplast H+-PPiase, provide the transmembrane proton motive force used by various secondary transporters. The widespread occurrence, taxonomically, of halophytes and the general paucity of information on the molecular regulation of tolerance mechanisms persuade us that research should be concentrated on a number of model species that are representative of the various mechanisms that might be involved in tolerance.

Salinity tolerance in halophytes

The increasing problem of global land salinisation and associated multibillion dollar losses in crop production require a better understanding of key physiological mechanisms conferring salinity tolerance in crops. The effective way of gaining such knowledge comes from studying halophytes. Halophytes have always attracted the attention of plant physiologists, due to their remarkable ability to tolerate and even benefit from salt concentrations that kill most other plant species. At the very least, halophytes may provide genes that allow transgenic conference of salinity tolerance to crops. In addition, some halophytes have already been tested as vegetable, forage and oilseed crops in agronomic field trials, whilst others already show good potential to be developed as crops. Surprisingly, our knowledge of fundamental ionic and molecular mechanisms conferring salinity tolerance in halophytes is rather limited and, at best, is restricted to several model species. This chapter summarises the current knowledge of physiological mechanisms regulating ion uptake and sequestration in halophytes. The following topics are covered: specific anatomical and morphological features of halophytes; tissue- and organ-specific ion compartmentation; mechanisms of osmotic adjustment in halophytes; radial ion transport in halophytes roots; mechanisms of Na+ and K+ loading into the xylem; Na+ sequestration in vacuoles in roots and leaf cells; ion transport in guard cells; control of ion fluxes into salt glands and bladders; and oxidative signalling and damage repair in halophytes. It is concluded that more in-depth electrophysiological and molecular studies are needed to reveal the identity of membrane transport systems and better understand what appears to be the complex and highly orchestrated regulation of ion transport and sequestration in halophytes.

Ion Transport in Halophytes

The salinization and water deficit of soil are widespread environmental problems in limiting plant survival, growth, and productivity. However, some plants could adopt some strategies to resist sal...

Osmotic adjustment and plant adaptation to environmental changes related to drought and salinity.

With the aim of determining whether grafting could improve salinity tolerance of tomato (Lycopersicon esculentum Mill.), and what characteristics of the rootstock were required to increase the salt tolerance of the shoot, a commercial tomato hybrid (cv. Jaguar) was grafted onto the roots of several tomato genotypes with different potentials to exclude saline ions. The rootstock effect was assessed by growing plants at different NaCl concentrations (0, 25, 50, and 75 mM NaCl) under greenhouse conditions, and by determining the fruit yield and the leaf physiological changes induced by the rootstock after 60 d and 90 d of salt treatment. The grafting process itself did not affect the fruit yield, as non-grafted plants of cv. Jaguar and those grafted onto their own root showed the same yield over time under non-saline conditions. However, grafting raised fruit yield in Jaguar on most rootstocks, although the positive effect induced by the rootstock was lower at 25mMNaCl than at 50 and 75mM NaCl. At these higher levels, the plants grafted onto Radja, Pera and the hybrid Volgogradskij3Pera increased their yields by ~80%, with respect to the Jaguar plants. The tolerance induced by the rootstock in the shoot was related to ionic rather than osmotic stress caused by salinity, as the differential fruit yield responses among graft combinations were mainly related to the different abilities of rootstocks to regulate the transport of saline ions. This was corroborated by the high negative correlation found between fruit yield and the leaf Na1 or Cl2 concentrations in salt-treated plants after 90 d of salt treatment. In conclusion, grafting provides an alternative way to enhance salt tolerance, determined as fruit yield, in the tomato, and evidence is reported that the rootstock is able to reduce ionic stress.

Grafting raises the salt tolerance of tomato through limiting the transport of sodium and chloride to the shoot

Programmed cell death (PCD) is a key element in normal plant growth and development which may also be induced by various abiotic and biotic stress factors including salt stress. In the present study, morphological, biochemical, and physiological responses of the theoretically immortal unicellular freshwater green alga Micrasterias denticulata were examined after salt (200 mM NaCl or 200 mM KCl) and osmotic stress induced by iso-osmotic sorbitol. KCl caused morphological changes such as cytoplasmic vacuolization, extreme deformation of mitochondria, and ultrastructural changes of Golgi and ER. However, prolonged salt stress (24 h) led to the degradation of organelles by autophagy, a special form of PCD, both in NaCl- and KCl-treated cells. This was indicated by the enclosure of organelles by ER-derived double membranes. DNA of NaCl- and KCl-stressed cells but not of sorbitol-treated cells showed a ladder-like pattern on agarose gel, which means that the ionic rather than the osmotic component of salt stress leads to the activation of the responsible endonuclease. DNA laddering during salt stress could be abrogated by addition of Zn 2+ . Neither cytochrome c release from mitochondria nor increase in caspase-3-like activity occurred after salt stress. Reactive oxygen species could be detected within 5 min after the onset of salt and osmotic stress. Respiration, photosynthetic activity, and pigment composition indicated an active metabolism which supports programmed rather than necrotic cell death in Micrasterias after salt stress.

Salt stress-induced cell death in the unicellular green alga Micrasterias denticulata.

Atriplex nummularia plants are able to grow well in the absence of significant amounts of Na+. Medium levels of salinity (100 mM NaCl or KCl) did not cause substantial inhibition of growth but increasing concentrations of salt induced a progressive decline in length and weight of the plants. This inhibition was significantly higher in KCl grown plants than in NaCl grown plants. In addition, although it has been proposed that both K+ and Na+ are involved in the osmotic adjustment of plants in response to high soil salinity, we show that Na+ ions contribute more efficiently than K+ ions to perform this function. Our results also indicate that most of the osmotic adjustment of the plant was due to the accumulation of inorganic ions. The strong inhibition of Rb+ transport caused by internal sodium suggests that this cation could be efficiently used by the plant and, as a consequence, the transport of other monovalent cations is down-regulated.

Effect of NaCl and KCl salts on the growth and solute accumulation of the halophyte Atriplex nummularia

Acts of Visitation: The Narrative of J.M. Coetzee

SummaryThis article points to the 17th-century Spanish writer, Miguel de Cervantes, as one important literary predecessor of the contemporary South African writer, J.M. Coetzee, a relation that has generally passed unnoticed among critics. This relation is brought to the foreground in Coetzee’s most recent novel, The Childhood of Jesus (2013), but it also underlies his previous ones, Age of Iron (1998), Disgrace (2000), and Slow Man (2005), as well as his critical pieces, “The Novel Today” (1988) and the “Jerusalem Prize Acceptance Speech” (1992b), all of which contain echoes of Cervantes’s masterpiece, Don Quixote ([1605, 1615]2005). My argument is that the conflict between imagination and reality, the novel and history, central in Coetzee’s fictional and non-fictional production, needs to be re-examined as a fundamentally Cervantine one. The adventures and fate of Don Quixote lie behind Coetzee’s exploration of whether literature may be an effective and ethical guide in our dealings with reality, whethe...

Miguel de Cervantes and J.M. Coetzee: An Unacknowledged Paternity

In his 1999 novel, Disgrace, J.M. Coetzee deals with both the perspicuous and subtle ways in which personal relationships in post-apartheid South Africa are conditioned by the persistent and entrenched legacy of apartheid and of centuries of racial inequality and oppression. However, and it is here that my analysis differs from those racialised readings the novel has received, Disgrace points to the fallacies of post-1994 ‘rainbowism’ by showing that inter-racial conflict is just one among the many others at work in South African society: the novel is pervaded by acts of violent intrusion that highlight the hostility and lack of understanding not only between blacks and whites, but also between different social groups such as landowners and tenants, country people and people from the city, men and women, parents and children, the old and the young, religious and non-religious people, and between human beings and animals. Simultaneously, we encounter acts of friendly visitation and hospitality that, on a m...

Can We Be Friends Here? Visitation and Hospitality in J.M. Coetzee's Disgrace

This chapter examines the male idealisation of the female figure that we find in many of J. M. Coetzee’s works, together with their depiction of male-female relationships as characterised by a constant conflict between the real and the ideal, imagination and physicality. Arguing that this conflict owes much to Don Quixote’s relation to Dulcinea, to which Coetzee’s texts repeatedly turn, Lopez analyses the ways in which Coetzee’s texts explore the complexities and ambivalent ethical consequences of passion and desire, which are often presented as undecidable forces exceeding the subject’s choice and control, but for which characters must take responsibility in social, ethical and legal terms.

María J. López

Papers

Effect of NaCl and KCl salts on the growth and solute accumulation of the halophyte Atriplex nummularia

Acts of Visitation: The Narrative of J.M. Coetzee

Miguel de Cervantes and J.M. Coetzee: An Unacknowledged Paternity

Can We Be Friends Here? Visitation and Hospitality in J.M. Coetzee's Disgrace

‘God Knows Whether There Is a Dulcinea in This World or Not’: Idealised Passion and Undecidable Desire in J. M. Coetzee