Main conclusion The heterologous expression of AtPCS1 in tobacco plants exposed to arsenic plus cadmium enhances phytochelatin levels, root As/Cd accumulation and pollutants detoxification, but does not prevent root cyto-histological damages. High phytochelatin (PC) levels may be involved in accumulation and detoxification of both cadmium (Cd) and arsenic (As) in numerous plants. Although polluted environments are frequently characterized by As and Cd coexistence, how increased PC levels affect the adaptation of the entire plant and the response of its cells/tissues to a combined contamination by As and Cd needs investigation. Consequently, we analyzed tobacco seedlings overexpressing Arabidopsis phytochelatin synthase1 gene (AtPCS1) exposed to As and/or Cd, to evaluate the levels of PCs and As/Cd, the cyto-histological modifications of the roots and the Cd/As leaf extrusion ability. When exposed to As and/or Cd the plants overexpressing AtPCS1 showed higher PC levels, As plus Cd root accumulation, and detoxification ability than the non-overexpressing plants, but a blocked Cd-extrusion from the leaf trichomes. In all genotypes, As, and Cd in particular, damaged lateral root apices, enhancing cell-vacuolization, causing thinning and stretching of endodermis initial cells. Alterations also occurred in the primary structure region of the lateral roots, i.e., cell wall lignification in the external cortex, cell hypertrophy in the inner cortex, crushing of endodermis and stele, and nuclear hypertrophy. Altogether, As and/or Cd caused damage to the lateral roots (and not to the primary one), with such damage not counteracted by AtPCS1 overexpression. The latter, however, positively affected accumulation and detoxification to both pollutants, highlighting that Cd/As accumulation and detoxification due to PCS1 activity do not reduce the cyto-histological damage.

Research is revealing an increasing number of positive effects of nature for humans. At the same time, biodiversity in cities, where most humans live, is often low or in decline. Tangible solutions are needed to increase urban biodiversity. Architecture is a key discipline that has considerable influence on the built‐up area of cities, thereby influencing urban biodiversity. In general, architects do not design for biodiversity. Conversely, urban conservation planning generally focuses on the limited space free of buildings and does not embrace architecture as an important discipline for the creation of urban green infrastructure. In this paper, we argue that the promotion of biodiversity needs to become a key driving force of architectural design. This requires a new multi‐species design paradigm that considers both human and non‐human needs. Such a design approach needs to maintain the standards of the architectural profession, including the aim to increase the well‐being of humans in buildings. Yet, it also needs to add other stakeholders, organisms such as animals, plants and even microbiota. New buildings designed for humans and other inhabitants can then increase biodiversity in cities and also increase the benefits that humans can derive from close proximity to nature. We review the challenges that this new design approach poses for both architecture and ecology and show that multi‐species‐design goes beyond existing approaches in architecture and ecology. The new design approach needs to make ecological knowledge available to the architectural design process, enabling practitioners to find architectural solutions that can facilitate synergies from a multi‐species perspective. We propose that a first step in creating such a multi‐species habitat is the design of buildings with an ecolope, a multi criteria‐designed building envelope that takes into account the needs of diverse organisms. Because there is no framework to design such an ecolope, we illustrate how multi‐species design needs to draw on knowledge from ecology, as well as architecture, and design computation. We discuss how architectures designed via a multi‐species approach can be an important step in establishing beneficial human–nature relationships in cities, and contribute to human well‐being and biodiversity conservation. Read the free Plain Language Summary for this article on the Journal blog.