Mother trees, altruistic fungi, and the perils of plant personification.

There are growing doubts about the true role of the common mycorrhizal networks (CMN or wood wide web) connecting the roots of trees in forests. We question the claims of a substantial carbon transfer from 'mother trees' to their offspring and nearby seedlings through the CMN. Recent reviews show that evidence for the 'mother tree concept' is inconclusive or absent. The origin of this concept seems to stem from a desire to humanize plant life but can lead to misunderstandings and false interpretations and may eventually harm rather than help the commendable cause of preserving forests. Two recent books serve as examples: The Hidden Life of Trees and Finding the Mother Tree.

Integrated information theory does not make plant consciousness more convincing.

It has been proposed by some plant scientists that plants are cognitive and conscious organisms, although this is a minority view. Here we present a brief summary of some of the arguments against this view, followed by a critique of an article in this same issue of Biochemical and Biophysical Research Communications by Calvo, Baluska, and Trewavas (2020) that cites Integrated Information Theory (IIT) as providing additional support for plant consciousness. The authors base their argument on the assumptions that all cells are conscious and that consciousness is confined to life. However, IIT allows for consciousness in various nonliving systems, and thus does not restrict consciousness to living organisms. Therefore, IIT cannot be used to prove plant consciousness, for which there is neither empirical evidence nor support from other, neuron-based, theories of consciousness.

Debunking a myth: plant consciousness.

Claims that plants have conscious experiences have increased in recent years and have received wide coverage, from the popular media to scientific journals. Such claims are misleading and have the potential to misdirect funding and governmental policy decisions. After defining basic, primary consciousness, we provide new arguments against 12 core claims made by the proponents of plant consciousness. Three important new conclusions of our study are (1) plants have not been shown to perform the proactive, anticipatory behaviors associated with consciousness, but only to sense and follow stimulus trails reactively; (2) electrophysiological signaling in plants serves immediate physiological functions rather than integrative-information processing as in nervous systems of animals, giving no indication of plant consciousness; (3) the controversial claim of classical Pavlovian learning in plants, even if correct, is irrelevant because this type of learning does not require consciousness. Finally, we present our own hypothesis, based on two logical assumptions, concerning which organisms possess consciousness. Our first assumption is that affective (emotional) consciousness is marked by an advanced capacity for operant learning about rewards and punishments. Our second assumption is that image-based conscious experience is marked by demonstrably mapped representations of the external environment within the body. Certain animals fit both of these criteria, but plants fit neither. We conclude that claims for plant consciousness are highly speculative and lack sound scientific support.

Plants Neither Possess nor Require Consciousness.

In claiming that plants have consciousness, 'plant neurobiologists' have consistently glossed over the remarkable degree of structural and functional complexity that the brain had to evolve for consciousness to emerge. Here, we outline a new hypothesis proposed by Feinberg and Mallat for the evolution of consciousness in animals. Based on a survey of the brain anatomy, functional complexity, and behaviors of a broad spectrum of animals, criteria were established for the emergence of consciousness. The only animals that satisfied these criteria were the vertebrates (including fish), arthropods (e.g., insects, crabs), and cephalopods (e.g., octopuses, squids). In light of Feinberg and Mallat's analysis, we consider the likelihood that plants, with their relative organizational simplicity and lack of neurons and brains, have consciousness to be effectively nil.

Interactions between a blue-green reversible photoreceptor and a separate UV-B receptor in stomatal guard cells.

Stomatal opening exhibits two main peaks of activity in the visible range-a red peak, mediated by photosynthesis, and a blue peak, mediated by one or more blue light (BL) photoreceptors. In addition, a pronounced peak in the UV-B region has been characterized, as has a smaller UV-A peak. The BL-induced stomatal opening can be reversed by green light (GL). Here we report that UV-B-induced opening is also antagonized by GL. To determine whether UV-B is being absorbed by the BL photoreceptor or by a separate UV-B receptor, the UV-B responses of two different Arabidopsis mutants, npq1 and phot1/phot2, were tested. Both putative BL-photoreceptor mutants exhibited normal stomatal opening in response to UV-B, consistent with the existence of a separate UV-B photoreceptor. Moreover, GL failed to antagonize UV-B-induced stomatal opening in the phot1/phot2 double mutant and only partially antagonized UV-B opening in npq1. Thus, both phot1 and phot 2, as well as zeaxanthin, are required for the normal GL inhibition of UV-B. A model for a photoreceptor network that regulates stomatal opening is presented. Unlike the situation in guard cells, the UV-B bending response of Arabidopsis hypocotyls during phototropism appears to be mediated by phototropins.

A simple nomenclature for a complex proton pump: VHA genes encode the vacuolar H(+)-ATPase.

The vacuolar-type H(+)-ATPase acidifies intracellular compartments and is essential for many processes, including cotransport, guard cell movement, development, and tolerance to environmental stress. We have identified at least 26 genes encoding subunits of the vacuolar-type H(+)-ATPase in the Arabidopsis thaliana genome, although inconsistent nomenclature of these genes is confusing. The pump consists of subunits A through H of the peripheral V(1) complex, and subunits a, c, c" and d of the V(o) membrane sector. Most V(1) subunits are encoded by a single gene, whereas V(o) subunits are encoded by multiple genes found in duplicated segments of the genome. We propose to name these genes VHA-x, where x represents the letter code for each subunit. Applying a consistent nomenclature will help us to understand how the expression, assembly and activity of this pump are integrated with plant growth, signaling, development and adaptation.

Identification, purification, and molecular cloning of N-1-naphthylphthalmic acid-binding plasma membrane-associated aminopeptidases from Arabidopsis.

Polar transport of the plant hormone auxin is regulated at the cellular level by inhibition of efflux from a plasma membrane (PM) carrier. Binding of the auxin transport inhibitor N-1-naphthylphthalamic acid (NPA) to a regulatory site associated with the carrier has been characterized, but the NPA-binding protein(s) have not been identified. Experimental disparities between levels of high-affinity NPA binding and auxin transport inhibition can be explained by the presence of a low-affinity binding site and in vivo hydrolysis of NPA. In Arabidopsis, colocalization of NPA amidase and aminopeptidase (AP) activities, inhibition of auxin transport by artificial beta-naphthylamide substrates, and saturable displacement of NPA by the AP inhibitor bestatin suggest that PM APs may be involved in both low-affinity NPA binding and hydrolysis. We report the purification and molecular cloning of NPA-binding PM APs and associated proteins from Arabidopsis. This is the first report of PM APs in plants. PM proteins were purified by gel permeation, anion exchange, and NPA affinity chromatography monitored for tyrosine-AP activity. Lower affinity fractions contained two orthologs of mammalian APs involved in signal transduction and cell surface-extracellular matrix interactions. AtAPM1 and ATAPP1 have substrate specificities and inhibitor sensitivities similar to their mammalian orthologs, and have temporal and spatial expression patterns consistent with previous in planta histochemical data. Copurifying proteins suggest that the APs interact with secreted cell surface and cell wall proline-rich proteins. AtAPM1 and AtAPP1 are encoded by single genes. In vitro translation products of ATAPM1 and AtAPP1 have enzymatic activities similar to those of native proteins.